A library for building and styling web components in pure-javascript.


Blocks.js is a view library - a set of extensible web components for building visual user interfaces and styling web applications in pure-javascript. Modular, composable web components. Modular, composable styles.

The power of functions and variables is unparalleled, and yet languages like HTML and CSS, which don't have any ability to compose structures together, are still the primary ways people build web applications. Framework after framework has come along to try and solve the problem of making web pages dynamic. Angular, Backbone, Ember, jQuery, mooTools, Dojo, YUI, etc have all tried to be everything to everyone. But what they fail at providing is simplicity and modularity. They end up with bloated libraries filled with features you're not using.

Blocks.js is here to change that. Finally, modern application development for the browser!

var Button = require("blocks.js/Button")
var Style = require("blocks.js/Style")
var Container = require("blocks.js/Container")

var list = Container()
;[1,2,3].forEach(function(n) {
    var text = "Hi "+n
    var toggleButton = Button(text) // create a button

    // make it do stuff when you click on it
    toggleButton.on('click', function() {
        if(toggleButton.text !== "RAWRR!!!") {
            toggleButton.text = "RAWRR!!!"
            toggleButton.state.set('color', 'rgb(128, 0, 0)')
        } else {
            toggleButton.text = text
            toggleButton.state.set('color', 'black')

    // add the button to the list

var greet = Button("send", "Send your Greetings") // labels like 'send' can differentiate otherwise identical types of blocks

// create styles with style objects .. = Style({
    border: '1px solid blue', // .. that use familiar css values,
    marginRight: 34,          // .. camelCase css properties and integers interpreted as "px" values when appropriate,

    Button: {                 // .. sub-block styles,
        $$firstChild: {       // .. pseudo-class styles,
            color: 'rgb(0,100,240)',
        $state: function(state) { // .. more sophisticated styling techniques
            return Style({
                color: state.color
    $send: {              // .. style based on an object's label, and ..
        color: 'green'

// append the list of buttons to the document body (so it shows up)

// custom blocks (use your favorite javascript class library - here proto is being used)
var NameInput = proto(Block, function() { // inherit from Block = 'NameInput' = function(LabelText) {              // the `build` method initializes the custom Block
        this.nameField = TextField()
        this.add(Text(LabelText), this.nameField)
        this.nameField.on('change', function() {
            list.children[0].text = "Hi "+this.val

var nameInput = NameInput("Your Name: ")
greet.on('click', function() {
    var text = Text("Whats up, "+nameInput.nameField.val+'?') = Style({display:'block'})

If anything in the documentation is unclear, or you want to see more examples, the unit tests give a comprehensive and exhaustive set of examples to look at.

Why use blocks.js?
  • Makes your web application easier to develop with modular reusable structure objects (Block objects) and Style objects
  • No HTML Needed. With blocks.js, you write in 100% javascript. The only html requirement is a document body. You can still add plain old HTML into your blocks using block.domNode.innerHTML tho if you so choose.
  • No CSS Needed. While blocks.js uses css style properties, it rejects the cascading nature of css, allowing one style to be fully isolated from another. No more wondering which selector in which stylesheet botched your nice clean style.
  • Works with your HTML and CSS. Blocks can be added as a child to any standard dom object and they can be styled with standard css stylesheets if you so choose.
  • Works with your current javascript. Blocks give you direct access to their domNode so you can use the dom manipulation libraries you're used to.
  • Fully separate style from structure. By using $state, $setup, and $kill javascript in your Style objects, you can include any javascript that is stylistic rather than structural.
  • Import Block modules with real APIs that anyone can release online. HTML snippets are so 1995.
  • Unlike HTML web components, blocks.js works in modern browsers without polyfills.
  • Also unlike HTML web components, element name collision isn't a problem.
  • Has a small footprint: 16.5KB minified and gzipped in umd format
Comparisons Install
npm install blocks.js

or download the built package blocks.umd.js from the 'dist' folder in the repository

var blocks = require('blocks.js')  // node.js and webpack

define(['blocks.umd.js'], function(blocks) { ... } // amd

<script src="blocks.umd.js"></script>
  blocks; // global 'blocks' module object


All blocks inherit from Block - the basic building-block of the system. Blocks are EventEmitters, and emitting events is one of the primary ways blocks should communicate.

Block is abstract and can't be instantiated on its own. See the section ''Custom Blocks'' for details on how to create objects that inherit from Block.


var Block = require("blocks.js") // or
var Block = require("blocks.js/Block") // or
blocks.Block // if you're using the umd package

Static properties and methods - The name of the Block. Used both for naming dom elements for view in browser dev tools and for styling.

Block.attach(listOfBlocks) - Appends the passed blocks to document.body. IMPORTANT: only attach a block to the dom via this attach function or a block's attach method. Without this, styles won't be rendered. Block.attach(domNode, listOfBlocks) - Appends the passed blocks to the passed domNode.

Block.detach(listOfBlocks) - Removes the passed blocks from their respective dom parents.

Block.createBody(callback) - Dynamically creates the body tag. Calls callback when done.

Instance properties and methods

block.parent - The Block's parent (which will also be a Block)
block.children - An array of the Block's children (which will all be Blocks themselves).
block.domNode - The Block's standard dom node object. block.label - A string used for styling. Should be set once when the object is instantiated, and cannot change. See the section on Style objects for details about how this is used.
block.excludeDomEvents - A set of dom events to exclude from automatic registration. Will have the structure {eventName1:1, eventName2:1, ...}. See the documentation for on for more details.
block.state - An observer object that can be listened on for changes. Can be used for any purpose, but is intended for being used to create dynamically changing styles. See the section on Style objects for an example.

block.add(block, block, ...) - Appends blocks as children to the calling block. This causes the domNodes of the passed blocks to be appended to the calling block's dom node.
block.add(listOfBlocks) - Same as above, but listOfBlocks is an array of Block objects.

block.addAt(index, block, block, ...) - Adds blocks as children to the calling block at a particular index.
block.addAt(index, listOfBlocks) - Same as above, but listOfBlocks is an array of Block objects.

block.addBefore(beforeChild, block, block, ...) - Adds blocks as children to the calling block before a particular child. If beforeChild is undefined, this will append the given nodes.
block.addBefore(beforeChild, listOfBlocks) - Same as above, but listOfBlocks is an array of Block objects.

block.remove(block, block, ...) - Removes the passed blocks as children.
block.remove(listOfBlocks) - Same as above, but listOfBlocks is an array of Block objects.
block.remove(index, index, ...) - Removes, as children, the blocks at the given indexes in the children list.
block.remove(listOfIndexes) - Same as above, but listOfIndexes is an array of indexes to remove.

block.attach(domNode=document.body) - Appends this Block's domNode to the passed domNode (default document.body). IMPORTANT: only attach a block to the dom via this attach function or a block's attach method. Without this, styles won't be rendered. block.detach() - Removes this Block's domNode from its dom parent.

block.attr(attributeName) - Return the value of the attribute named attributeName on the Block's domNode.
block.attr(attributeName, value) - Sets the attribute to the passed value.
block.attr(attributeObject) - Sets the attributes in the attributeObject, where attributeObject looks like: {attribute1: value1, attribute2: value2, ...}. - Holds the object's Style object. Starts out undefined, and can be set to undefined to remove a Style that has been set. Changing this property triggers style affects in the Block's children.
block.visible - Setting this variable to false hides the block using "display: none;". Setting this variable to true unhides it. Accessing the variable will return its visibility state.
block.focus - Setting this variable to true gives the block focus on the page. Setting this variable to false blurs it. Accessing the variable returns whether or not the block is the focused element on the page.

block.selectionRange - Returns an array representing the selection range in terms of visible character offsets. E.g. a value of [2,4] means that the current element has 2 visible entities (usually characters) selected within it at offset 2 and 4 from the start. Note that if there are hidden characters like multiple spaces in a row, or newlines, or other non-visible characters (mostly only applies to contenteditable nodes), they are ignored.
block.selectionRange = [offsetStart, offsetEnd] - Setting the selectionRange property sets the selection inside the Block's domNode based on the given offsets.

Example of selectionRange:

var x = Text("You're not my buddy, guy")
x.selectionRange = [0,6] // selects "You're"

Instance properties inherited from EventEmitter

All methods and properties from EventEmitter are inherited by Block. The important ones:

block.emit(event, data, data2, ...) - Emits an event that triggers handlers setup via the Block's on methods.

block.on(event, callback) - Registers a callback that will be called when the passed event is emitted by the Block.

  • event - The string event name to listen for. If the passed event is one of the many standard dom events (e.g. 'click', 'mouseover', 'touchstart', etc), the passed handler will be registered as a dom event handler in one of three cases:
    • the block's excludeDomEvents object is undefined
    • the event is in the block's excludeDomEvents property
  • callback(data, data2, ...) - the callback gets any arguments passed to emit after the event name.

block.once(event, callback) - Like on but the callback will only be called the first time the event happens., callback) - Removes a callback as an event handler (the callback won't be called for that event again).
block.removeListener(event,callback) - Same as off.

this.removeAllListeners(event) - Removes all the callbacks for the passed event.
this.removeAllListeners() - Removes all callbacks.

Instance properties inherited from EventEmitterB


The ifon and related methods are useful primarily for performance reasons. They allow registering event listeners only when they're needed, so that the browser doesn't get overloaded with event handlers. Its recommended that ifon is used whenever possible. An example:

var text = Text("CLICK ME")
var parent = Container(text)

var handler;
parent.ifon('someoneClickedTheThing', function() {
    text.on('click', handler = function() {
        parent.emit('someoneClickedTheThing', "I can't believe it")
parent.ifoff('someoneClickedTheThing', function() {'click', handler)

block.ifon(event, callback) - Registers a callback that will be called when a handler is registered for event if it had no handler registered previously. If there is already a listener attached to that event, callback is called immediately.

  • callback(event) - The callback gets the newly registered event type as its argument.

block.ifoff(event, callback) - Registers a callback that will be called when the last handler for event is unregistered.
block.ifoff(callback) - Registers a callback that will be called when the last handler for any event is unregistered.

  • callback(event) - The callback gets the unregistered event type as its argument.

block.removeIfon() - Removes all ifon handlers.
block.removeIfon(event) - Removes all ifon handlers for the passed event.
block.removeIfon(callback) - Removes callback as an "all" ifon handler (a callback passed to ifon without an event).
block.removeIfon(event, callback) - Removes callback as an ifon handler for the passed event.

block.removeIfoff() - Removes all ifoff handlers.
block.removeIfoff(event) - Removes all ifoff handlers for the passed event.
block.removeIfoff(callback) - Removes callback as an "all" ifoff handler (a callback passed to ifoff without an event).
block.removeIfoff(event, callback) - Removes callback as an ifoff handler for the passed event.


The proxy method uses ifon and ifoff to minmize the number of event listeners that need to be attached in the system.

block.proxy(emitter, options) - Proxies event registration to emitter.

  • emitter - The emitter (usually a Block) to proxy handler binding to
  • options - An object that defines what events are proxied. If undefined, all events are proxied. The object can have one of the following properties:
    • only - An array of events to proxy.
    • except - An array of events to not proxy. All other events are proxied.

Example of proxy:

var A = Text()
var B = Text()

A.on("click", function() {
    console.log("hey hey heyyy! "+3)

B.emit("click", "Ughh..") // console prints "hey hey heyyy! Ughh.."

Instance events

"newParent" - Emitted when a Block gets a new parent. Note: this event is used by Style objects, so don't prevent these events.
"parentRemoved" - Emitted when a Block is detached from its parent. Note: this event is used by Style objects, so don't prevent these events.

Dom Events

Block object will emit any standard dom event ("click", "mousedown", "keypress", etc) when listened on. Note that a Block doesn't add an event listener to the dom node until someone listens on that event on the block. This minimizes the number of event listeners that are registered on the page. To see the list of dom events this applies to (supposed to be all of them), see the top of src/node_modules/Block.js

Custom Blocks

Blocks.js is all about custom blocks. That's the point: your application should be built as a composition of custom blocks on top of custom blocks so that, instead of a million divs, you have semantically appropriate javascript web components.

In this documentation, we're going to be using the class library proto. The descriptions here apply to both inheriting from Block and inheriting from any of the standard blocks. There are a couple special properties to create when making a custom Block:

  • name - The name is a required property, should be named whatever your class is named, and should be a somewhat unique name in your system (tho it isn't required to be unique).
  • build() - The "sub-constructor". The constructor calls this method, passing all arguments, to the build method. The return value of build is ignored.
  • defaultStyle - If set to a Style object, the style object will be the block's default style. Unlike explicitly set Styles and inherited Styles, css properties in defaultStyle do cascade line-by-line. Also, if a block inherits from another Block class that also has a defaultStyle, the default styles mix together with the child Block class style properties overriding the parent Block class's default properties. So in the below example, if block is given a style that defines color: green, it's fontWeight will still be 'bold'.

For example:

var CustomBlock = proto(Block, function() { = "CustomBlock"
    this.defaultStyle = Style({
       color: 'red',
       fontWeight: 'bold'
    }) = function(x) {
        this.x = x

var block = CustomBlock(5) // block.x is 5

Releasing custom blocks as separate modules

If you'd like to release a custom Block or set of Block objects, there are a couple of important things to remember to do:

  • If you're releasing on npm, do not add blocks.js as a normal "dependency". Instead, it should be added as a "peerDependency" or perhaps a "devDependency". It shouldn't be a normal "dependency" because otherwise bundlers may bundle multiple copies of blocks.js when using your custom block module (even though bundlers like webpack dedupe files, if the versions of webpack being used are slightly different, they would still package together both versions of blocks.js)
  • If you're releasing a module distribution intended to be loaded in a <script> tag, do not bundle blocks.js in your distribution bundle. It should assume the blocks global variable (e.g. blocks.Block) is available.

Inheriting from Blocks with a class library other than proto

If you're building Blocks with something other than proto (or are using a version of proto older than 1.0.17), note that blocks.js relies on the following properties:

  • block.constructor - must point to the Block prototype class (in the proto example, the object returned by the call to proto). This is a standard property that all good class libraries should set.
  • block.constructor.parent - must point either to the parent of the block's constructor, or undefined if there is no parent. Note that while proto sets this automatically, it is not a standard property and if you're using a different library from proto, you must set this manually.
  • - the constructors must have the same name property that instances can access. Note that while proto sets this appropriately, most class libraries probably don't and it isn't simple to manually set. See here for details.

Also, make sure that Block's constructor is called on new instances that inherit from Block.

Inheriting from Blocks without a class library

Properly subclassing a prototype in javascript isn't the simplest thing to do, but if you want to do it, here's how:

var CustomBlock = function() { // Block's constructor must be called
CustomBlock.parent = Block // needed for correct Style rendering

var Intermediate = function(){}; Intermediate.prototype = Block.prototype
CustomBlock.prototype = new Intermediate() = 'CustomBlock'       // the name is a required property
CustomBlock.prototype.constructor = CustomBlock  // required for correct Style rendering, and is a standard javascript convention = function(constructorArgument1, constructorArgument2, ...) {
    // .. custom constructor code
CustomBlock.prototype.customMethod = function() {
    // ...

Standard Blocks

The built-in standard blocks all inherit from Block and so have all the methods and properties in the above documentation. For each build-in block, its name property will be the same as the name the documentation uses for it. For example Button will have the name "Button".

To use these built in blocks, access them via either require("blocks.js/<BlockName>") or blocks.<BlockName>. For example:

var Table = require("blocks.js/Table") // webpack or browserify
// or
var Table = blocks.Table // if loading the umd bundle in a <script> tag


There are some conventions that can help you learn to use standard Blocks, and help make custom Blocks you build more easily understood. These conventional properties, constructor parameters, and behavior are encouraged to be used in custom Blocks built by you, especially if you're planning on open-sourcing them.

Every standard Block has an optional first parameter label. This makes it easy and non-intrusive to label parts of your custom Blocks for easy styling.

In as many cases as possible, Blocks will use properties defined with getters and setters rather than using methods. There are a few standard properties that some blocks have:

  • text - Gets and sets some visual text that a Block has. Button, Text, and Select.Option have this property.
  • selected - Gets and sets the selected-state of the Block. CheckBox, Select.Option, and Radio.Button have this property.
  • val - Gets and sets some value that a block has. This will never be the same as either text or selected. Radio, Select, TextArea, and TextField all have this property.

This is a standard event that many blocks can emit:

  • change - Emitted when an important value of a block changes. This will always be either the block's val property or its selected property (but never both). Change events won't have any information passed with them - you can access the object itself if you need data from it.

Some blocks have sub-blocks specifically related to them. For example, Select has Option blocks, and Table has Row and Header blocks, and Row and Header have Cell blocks respectively.

  • There will also be a property with the name of the sub-block, but lower-case and plural, that contains either a map or a list of the sub-objects. For example, Select has an options map.
  • For these types of blocks, there will be a method on the main block (examples of main blocks: Select or Table) to create a new sub-block (e.g. Option or Row), append it to the calling block, and returns that sub-block. The method will be named the same as the sub-block but in lower-case (e.g. selectBlock.option(...) will return an Option block).


Your standard html <button>.

Button(text) - Returns a new button that has the passed text.
Button(label, text)

button.text - Sets or gets the button's text.


Your standard html <canvas>.

Canvas(height, width) - Returns a new Canvas object that has the passed dimensions.
Canvas(label, height, width)

canvas.height - Sets and gets the canvas's height.
canvas.width - Sets and gets the canvas's width.

canvas.context(type, attributes) - Returns a standard canvas context. The type and attribute parameters and return value are the same as the html-standard getContext.

canvas.toImg - Returns a data-url representing the image currently drawn on the canvas.
canvas.toDataURL - Same as canvas.toImg.


Your standard html <input type="checkbox">.

CheckBox() - Returns a new unchecked CheckBox.

checkbox.selected - Sets and gets the checkbox's selected state (true for selected, false for unselected).


A <div> that contains other blocks.

Container(block, block, ...) - Returns a new container with all the passed blocks as children (in the passed order).
Container(listOfBlocks) - Same as above except listOfBlocks is an array of blocks.
Container(label, block, block, ...)
Container(label, listOfBlocks)


Your standard html <img>.

Image() - Returns a new empty image.
Image(imageSource) - Returns a new image with the passed imageSource.
Image(label, imageSource)

image.src - Gets or changes the image's source.


An <ol> or <ul> element.

List() - Returns a new empty list.
List(ordered) - Returns a new empty list. Is an ordered-list if ordered is true, and an unorderd-list otherwise.
List(listInit) - Returns a new populated list. listInit is an array containing either Block objects or strings to add as list items. List(ordered, listInit)
List(label, ordered)
List(label, listInit)
List(label, ordered, listInit)

list.item(contents) - Creates a new ListItem with the passed contents and appends it to the list, which can either be a Block or a string.
list.item(label, contents)

List.Item - The ListItem class.

List.Item(contents) - same as list.item above, except doesn't append the item to any list.
List.Item(label, contents)

Radio - Not a Block

A set of radio buttons. Radio itself is not a Block, but rather contains a set of related RadioButtons (which are Block objects).

Radio() - Returns a new Radio object where a button is not required to be set (same as Radio(false)).
Radio(required) - Returns a new Radio object. If required is true, a radio button will always be selected (and buttons cannot be deselected), otherwise radio-buttons can be deselected, and no radio button is selected by default.

radio.button(value) - Creates a new RadioButton with the passed string value that is a member of the Radio object.
radio.button(label, value)

radio.selected - Returns the RadioButton object that is selected.
radio.val - Gets the value of the RadioButton that's selected, or selects the RadioButton that has the set value (e.g. radio.val = 'elvis' would select the radio button with the value "elvis")

radio.remove(radioButton, radioButton, ...) - Removes the passed radio buttons from the Radio object's set. Note that this will not remove the buttons from the page - that must be done separately for whatever Block contains the RadioButtons.
radio.remove(arrayOfRadioButtons) - Same as above, except the argument is an array of the RadioButtons to remove.
radio.remove(value, value, ...) - Removes the radio buttons that have the passed values from the Radio object's set.
radio.remove(arrayOfValues) - Same as above, except the argument is an array of the values who's radio buttons should be removed.

Radio.Button - The RadioButton class.

radioButton.val - Gets or sets the value of the radio button.
radioButton.selected - Gets whether the radio button is selected or not. If set to true, selects the button. If set to false, deselects it.
radioButton.selectNext() - Sets the next radio button in the Radio object's set.
radioButton.selectPrevious() - Sets the previous radio button in the Radio object's set.


Your standard <select> element.

Select() - Returns a new empty selection list.
Select(selections) - Returns a new populated selection list.
Select(label, selections)

  • selections - An object with the structure {optionValue: optionText, ...}

select.option(value, text) - Creates a new Option with the passed value and text, and appends it to the list.
select.option(label, value, text)

select.val - Gets the value of the selected Option, or selects the Option with the set value (e.g. select.val = 'moo' selects the Option with the value 'moo').

Select.Option - The Option class.

Select.Option(value, text) - same as select.option above, except doesn't append the Option to any list. Select.Option(label, contents)

option.selected - Gets or sets the selected state of the Option.
option.text - Gets or sets the display text of the Option.
option.val - Gets or sets the string value of the Option.


Your standard <table> element.

Table() - Returns a new empty table.
Table(tableInit) - Returns a new populated table.

  • tableInit - A list where each element in the list represents a row. Each element itself should be a list where each element is a Block or string to put in a table Cell. E.g. Table([['a','b','c'],[Text('x'),Text('y')]]) is a table with two rows and three columns, where there are only two cells in the second row.

table.row(rowInit) - Creates a new table TableRow (<tr>), and appends it to the table.
table.row(label, rowInit)
table.header(rowInit) - Creates a new table TableHeader (<th>), and appends it to the table.
table.header(label, rowInit)

  • rowInit - A list where each element is a Block or string to put in a table TableCell. E.g. table.row(['a','b','c']) is a row with three cells.

Table.Row - The TableRow class.
Table.Header - The TableHeader class.
Table.TableCell - The TableCell class.

Table.Row(rowInit) - same as table.row above, except doesn't append the TableRow to any table.
Table.Row(label, rowInit)
Table.Header(rowInit) - same as table.header above, except doesn't append the TableHeader to any table.
Table.Header(label, rowInit)

row.cell(contents) - Creates a new table TableCell (<td>) and appends it to the TableRow.
row.cell(label, contents)
header.cell(contents) - Creates a new table TableCell (<td>) and appends it to the TableHeader.
header.cell(label, contents)

  • contents - Either a string (text content) or any value you could pass into block.add (a Block, a list of Blocks, etc).

Table.Cell(contents) - Same as row.cell, but doesn't append the cell to any row. Table.Cell(label, contents)

cell.colspan(columns) - Sets the column-span (colspan attribute) of the cell.


A <div> with text in it.

Text() - Returns an empty Text object.
Text(text) - Returns a Text object populated with the passed string text.
Text(label, text)

text.text - Sets or gets the object's text.


A multi-line text input field. Your standard <textarea> element.

TextArea() - Returns an empty TextArea. TextArea(label)

textArea.val - Gets or sets the testArea's value (the text inside the text box).


A one-line text input field. Your standard <input type='text'> element.

TextField() - Returns an empty TextField.
TextField(password) - Returns an empty TextField with the password attribute, meaning any text inside the box will be displayed so that only the number of characters can be seen, and not the characters themselves.
TextField(label, password)

textField.val - Gets or sets the textField's value (the text inside the text box).

Style objects

If you're going to build a web application, why not do it with Style?

While a Block is pretty analogous to its HTML node, Style objects in blocks.js are quite different from normal CSS.

In blocks.js, individual css style properties do not cascade. Instead, whole Style objects cascade. This may not seem like much of a difference, but it makes all the difference. For example:

var parentContainer = Container([
]) = Style({
    Text: {           // 1
        color: 'blue',
        fontWeight: 'bold'
    Container: {
        Text: {       // 2
            color: 'red'

In the above example, "a" will be bold and blue, and "b" and "c" will be red. But "b" and "c" won't be bold - that property does not cascade. The Text styling inside Container is isolated from all previous stylings of Text, which means you don't have to worry about the styles someone used for elements further up the dom tree. I mentioned, tho, that whole Style objects do cascade, and that is why "d" will also be blue and bold even though it isn't a direct child of parentContainer.

Another difference is that blocks.js doesn't have selectors that can style any element on the page. Traditional CSS stylesheets are developed by selecting a group of elements from the entire page (via ids, classes, attributes, pseudoclasses representing element state, etc) and appending styles to them. These styles may overwrite styles written earlier, and they themselves may be overwritten. In blocks.js, Style objects can only be attached in a strict hierarchical setting, where only a specific section of the dom can be affected. In the above example, the Text style marked 2 doesn't affect anything outside that inner Container. For example, even though the text "d" is a Text object inside a Container object, it is not colored red. That's because styles in blocks.js are not like the selectors you're used to from css. They are strictly hierarchical - they only affect descendant Block objects' (children, grandchildren, etc) from the point in the dom they match.

The combination of the fact that blocks.js Style objects only cascade as a whole object and that styles are defined hierarchically makes styles modular and provides isolation from other styles on the page, so that it becomes much easier to understand and manage styling for a page or entire application.

Style constructor

Style(styleDefinition) - Creates a Style object.

  • styleDefinition is an object where key-value pairs can be either style properties or selectors:
    • style properties:
      • <cssPropertyName>: the value is a valid css value for that style property.
      • $setup: the value is a function to be run on a block when the style is applied to it
      • $kill: the value is a function to be run on a block when a style is removed from it
      • $state: the value is a function to be run when block.state changes (ie when its change event fires).
    • selectors - the value for each of these should be a Style object or a nested styleDefinition object
      • <BlockName>
      • $<label>
      • $$<pseudoclass>
    • $inherit


This type of key-value pair is simple - just your basic css style. Example:

    color: 'rgb(100, 200, 50)',
    marginRight: 3

The above style would give a color and margin-right to whatever Block is set with that style ( = styleObject). Note that camelCase names can be used, and numbers are automatically appended with "px" if appropriate for the property (just like with jquery's css method).

$setup and $kill

$setup(block) is a function that is run when the style is applied to a block, and $kill(block, setupObject) is run when the style is removed from a block. Both functions get the block being given the style as their first argument, the $kill also gets the return value of the $setup function as its second argument. For example:

var S = Style({
    $setup: function(block) {
        block.text = "I got zee style"
        return 20
    $kill: function(block,setupValue) {
        block.text = "I'm "+setupValue+"% less cool"
var t = Text("x") = S
t.text === "I got zee style" = undefined
t.text === "I'm 20% less cool"


$state(state) is a function that is run when the block's state observer property emits a change event (which happens when its changed with its methods set, push, splice, or append). The state function is passed the value of block.state.subject as its parameter. The return value of the function should be a Style object to mix with the object's current style.

Note that if you create styles in $state functions, remember that you will create a new style every time the state changes. This may be a problem with some applications that have a lot of state changes, or particularly rapid state changes (its unclear at what point this could cause problems).


var c = Text("hi")

var colorStyles = {
    yellow: Style({backgroundColor: 'yellow'}),
    red: Style({backgroundColor: 'red'}),
    green: Style({backgroundColor: 'green'})
} = Style({
    color: 'blue',
    $state: function(state) {
        if(state.success) {
            if(state.late) {
                return colorStyles.yellow
            } else {
        } else {

c.state.set("success", true) // container's background turns green
c.state.set("late", true)    // container's background turns yellow

In the above example, the container goes through all 3 backgroundColor colors as its state changes. In all states, the text color will be blue tho, since the $state style mixes with the primary style properties.


This sets a style for the Block with the given name. Only blocks within the block who's style this is are affected, blocks that do not descend from the styled block, and even the styled block themselves are not affected. For example:

var stylish = Style({
    Text: {
        color: 'red'

var container = Container([Text('a')])
var text = Text("b") = stylish = stylish

In the above example, only "a" is styled red. The Text "b" remains the default, black.

You can also give Blocks a Style object, which is the same as the above form, except that the object-immediate is passed into the Style constructor:

var textStyle = Style({
    color: 'red'

var stylish = Style({
    Text: textStyle

Keep in mind that Block styles are inherited by their parent in-full (not line-by-line like in css). So any Block that isn't given its own explicit style inherits from its ancestors (if its ancestors have a style for that Block). For example,

var a,b,c,d,e, dContainer
var tree = Container([
    a = Text('a'),
        b = Text('b'),
        c = Text('c'),
        dContainer = Container([
            d = Text('d'),
                e = Text('e')
]) = Style({
    Text: {color: 'green'}
}) = Style({
    fontWeight: 'bold'
}) = Style({
    Text: {textDecoration: 'underline'}

I hope you don't mind I assigned variables inside the Block structure - don't worry, the structure would be the same if the variables weren't assigned, but assigning the variables allows me to manipulate them after the structure is defined.

In any case, in the above example, the tree object is given a style where Text blocks are green. However, dContainer is given an alternate Text style. How does that affect the resulting style? Well, "a" and "b" are colored green, but "d" and "e" are not green. Instead, "d" and "e" are the default color, black, and are underlined. This is because "d" and "e" inherit the Text style from dContainer which overrides the Text style given to tree. And what about "c" you ask? Since "c" is given its own explicit style, that style also overrides any inheriting style. So "c" is bold and the default black.


Block objects can be given a label property, which can be used to identify Block objects of the same type that have different purposes within their parent. This is essentially analogous to giving divs class names, and then styling using that class, except that it works in blocks.js's hierarchical way of course. Note, tho, that a Block can have only one label. For example:

var container = Container([
    Text("header", "Your Receipt, Sir: "),
    Text("receipt", "1 bagel - $5, 3 buffulo - $45, 3 sticks dynamite - $100, 45 tons of wheat - $200")
    Text("Thank you for using butler-copter!")
]) = Style({
    Text: {
        fontWeight: 'bold',
        color: 'blue'
    $header: {color: 'gray'},
    $receipt: {color: 'green'}

In the above example, the text "Your Receipt, Sir: " will be gray, the receipt text will be green, and the thank-you text will be blue. Only the thank-you text will be bold.

Note that $label styles override block styles, even if the block style is "closer" to the block. For example, in the following example, the text "hi" will be gray, not blue.

var container = Container([
]) = Style({
    $someLabel: {color: 'gray'},
    Container: {
        Text: {color: 'blue'}


Pseudoclasses filter out which Block styles are given to. Also, the styles mix with the styles defined in the style-definition containing it. For example:

var x = Text("hi") = Style({
    fontWeight: 'bold',
    $$hover: {color: 'red'}

The above code changes the text from bold-black to bold-red when you hover over it, and back to black again when you move your mouse off the text.

Pseudoclasses also mix with each other when applicable. For example:

var container = Container([Text("a"), Text("b")]) = Style({
    Text: {
        $$lastChild: 'bold',
        $$hover: {color: 'red'}

In the above code, "a" will start black and change to red when you hover over it. "b" will start black and bold, but will change to red and bold when you hover over it.

To set a style only when multiple pseudoclasses apply, simply nest them. For example:

var text = Text("a") = Style({
    $$lastChild: {
        $$hover: {color: 'red'}

In the above code, "a" will turn red if it is both the last child of its parent and is hovered over.

Also, pseudoclasses may take parameters, which are passed in with parens like a javascript function. For example:

var c = Container([Text("a"),Text("b"),Text("c"),Text("d"),Text("e")]) = Style({
    Text: {
        '$$nthChild(1+2n)': {color: 'red'},

In the above code, "a", "c", and "e" are red, while "b" and "d" are black (the default).


The $inherit property, if set to true, indicates that the style inherits properties from the style "above" it - the style that would be used if the current style wasn't there. For example in the following, the text inside the container gets a green background, but also a red text color:

    Text: {color: 'red'},
    Container: {
        Text: {
            $inherit: true,
            backgroundColor: 'green'

In the following, a Text block with the label 'boom' would have both a green background and red text, whereas a Text block without that label, would not have the background color:

    Text: {color: 'red'},
    $boom: {
        $inherit: true,
        backgroundColor: 'green'

Note that $inherit is ignored the top-level of psuedoclass styles, $state styles, and defaultStyles since they always inherit.

Combining them together

Style objects can be as simple as a few standard css properties, or can take the place of a whole css stylesheet and more. Here's an example of a more complex style:

var topBarHeight = 100

    marginTop: topBarHeight,
    Button: {
        $setup: function(block) {
            var handler;
            block.on('moo', handler=function() {
                console.log("He won't stop mooing!")
            return {handler:handler}
        $kill: function(block, setupState) {

    $closeButton: {
        //future: $inherit: true, // inherits the Button style (if the block is a Button)
        position: 'absolute',
        right: 3, top: 3,
        width: 'calc(50% - 2px)'

    Table: {
        TableHeader: {
            TableCell: {
                borderBottom:'1px solid #000'
        TableRow: {
                TableCell: {
                    borderTop: '1px solid #000'
            TableCell: {
                '$$nthChild(1)': {
                    borderLeft: "1px solid #000"
                $$lastChild: {
                    borderRight: "1px solid #000"
            $$lastChild: {
                TableCell: {
                    borderBottom: "1px solid #000",
                    '$$nthChild(1)': {
                        borderLeft: "1px solid #000",
                        borderRight: "1px solid #000",

    TopBar: {
        marginTop: -topBarHeight+2,
        position: 'absolute',
        right: 0,

        Search: {
            position: 'relative',
            top: -3,

                 height: 23

        DropTab: {
            position: 'static',

            $wrapper: {
                position: 'static'

            $menu: {
                position: 'absolute',
                border: border,
                marginTop: 1,
                backgroundColor: 'white',
                cursor: 'pointer',

                Text: {
                    color: 'bonkers'
            $button: {
                border: border,
                fontSize: 24,
                fontWeight: 'bold'

        $userDropTab: {
            //future: $inherit: true, inherits from DropTab above
            cursor: 'pointer'


styleObject.mix(styleObject2) styleObject.mix(styleDefinition)

Returns a new style that combines together calling style object and the passed style object or style definition. The properties from the passed style object override the ones from the calling object.


var newStyle = oldStyle.mix({
   color: 'red'
var newStyle2 = oldStyle.mix(anotherStyle)


Returns a new style that is a copy of the calling style object but has a new className. Written for internal use.


Style.addPseudoClass(name, fns) - Creates a new pseudoclass that can be used in Style objects. This can be used to create all-new psuedoclasses no one's ever thought of before!

  • name - The name of the new pseudoclass
  • fns - An object with the members:
    • check(block, processedParameter) - A function that returns true if the pseudoclass applies to passed block
    • setup(block, startCallback, endCallback, processedParameter) - A function that should call startCallback() when the pseudoclass starts applying, and endCallback() when it stops applying. Can return a state object that will be passed to the kill function.
      • processedParameter - The parameter passed to the pseudoclass (e.g. in ":not(:first-child)", ":first-child" is the parameter). If a processParameter function is given, this will be the return value of that function.
    • kill(block, state) - A function that cleans up any event listeners or anything else set up in the setup function.
    • emulated - (Optional - default false) Set to true if this implements a native pseudoclass. If true, Blocks will attempt optimize the pseudoclass using native css if possible.
    • processParameter(parameter) - (Optional) Takes the pseudoclass parameter and returns some object representing it that will be used by the setup and check functions.
    • parameterTransform(parameter) - (Optional) Returns a modified version of the passed parameter. This is useful in cases where native pseudoclass parameter parsing is unnecessarily strict (eg. nth-child parameters)

Standard Pseudoclasses

Any pseudoclass that exists in standard css can be used by blocks.js, even if it isn't build-in with a js-rendered emulation. The catch is that their use is limited. The following things aren't supported for these:

  • Using a $setup, $kill, or $state functions within the pseudoclass style definition
  • Using non-standard pseudoclasses within the pseudoclass style definition

Built-in JS Rendered Pseudoclasses

  • hover - The usual :hover pseudoclass
  • checked - The usual :checked pseudoclass
  • required - The usual :required pseudoclass
  • lastChild - The usual :last-child pseudoclass
  • nthChild(a+bn) - The usual :nth-child pseudoclass (with more tolerant parameter parsing)

Note that, while the list of built-in pseudoclasses is currently short, all standard pseudoclasses can be defined except the ":visited" pseudoclass, because the necessary information is not available via javascript (a browser "security" policy).

Default style

Blocks.js unifies the default styles of dom nodes - all objects that inherit directly from Block have the same default styling unless they define their defaultStyle property.

The base default is mostly the same as css's base default. The two defaults that are different for Block objects:

  • display - "inline-block"
  • position - "relative"
  • box-sizing - "border-box" (excepting <img> nodes, which are still defaulted to content-box because pixel perfect image sizing is often important)

Also, while most css styles are not inherited from a Block's parent, the following are inherited:

  • color
  • cursor
  • fontFamily
  • fontSize
  • fontStyle
  • fontVariant
  • fontWeight
  • visibility

And while blocks.js generally rejects css's use of cascading, there is some similar cascading going on, but much more simplified and localized. Defining this behavior in terms of "cascading order" (where later additions override earlier), the order is:

  1. The base default style (described above in this section).
  2. The defaultStyle property of the block instance's furthest ancestor class
  3. ... (more defaultStyles in the Block's ancestry)
  4. The defaultStyle property of the Block's parent class
  5. The defaultStyle property of the Block itself
  6. The Block instance's current style (either an inherited style or its style property)
  7. The state style returned for that block by its current style
  8. Any pseudoclass styles that apply on the block

Tips and Recommendations

Don't Create a node until you need it

Often in traditional web development, all the HTML will be rendered and any javascript for them initialized on page load, and the elements that shouldn't be shown to the user are simply hidden, and then shown when needed. Using blocks.js, its recommended that you create and remove nodes as needed, rather than showing and hiding (using visible). The only reason to use the show/hide technique is if the element in question is particularly expensive to generate.

  • Block.label is not dynamic (can't be changed) because it is intended to be used to identify a particular Block when multiple Blocks of the same type are used alongside eachother. If you're looking for a way to change styles dynamically, use Block.state.
  • Blocks are styled based on their name rather than their object identity (which would be possible with an array style definition like [Text,{backgroundColor:'...'}]) because otherwise all Blocks would have to be exposed at the top level. Not only does this go against modularity, but creators of 3rd party modules would inevitably fail to expose all their Blocks, which would make styling impossible. With names, you don't have to be able to reach the object, you just have to know its name.
  • don't use npm shrinkwrap for browser modules like this, because otherwise multiple minor versions of the same package might get into a browser bundle and make page loading slower
What blocks.js is not

Blocks.js is not:

  • a compatibility layer. Blocks.js uses modern browser features and is built to rely on polyfills to add older browser support. If you're looking for a compatibility system, try modernizr.
  • a path router. If you're looking for a path routing module, try grapetree.
  • a class system. If you're looking for a system for creating classes and prototypes, try proto.
  • a module system, script bundler, or loader. If you're looking for an excellent module system and bundler, look no further than webpack.
  • a templating system. In blocks.js, you use functions and objects to compose together a page, rather than templates.
  • an animation library. If you're looking for animations, try Émile.
  • a framework. A framework is a system that calls your code. A module is a set of functions and classes that your code can call. Blocks.js is the latter. Blocks.js can work well right alongside traditionally written html and css, and you can choose to wrap dom constructs in a Block only if you want to.
  • super heroic. It does one thing well: web components. It embraces the single-responsibility principle and is entirely stand-alone.
  • Billy Tetrud
  • Robbert Wijtman - designed and helped implement the prototype version of blocks.js
  • have an event a block will emit when it or one of its ancestors becomes detached from the dom

    • Think about what to do about event forwarding for such an event, and for the 'newParent' and "parentRemoved' events - they shouldn't be forwarded
  • consider adding vertical-align:top to the default css, since it solves weird issues with inline-blocks causing extra bottom-margin:

  • Implement an $inherit option on Styles, so that they can implicitly inherit from styles above them without specifying which style to combine into it

  • Emulate the :not psuedoclass

  • Figure out how to support animations, @keyframes and that kind of thing

  • support css animations

  • Maybe if a block has an explicit style set, it ignore's any styling from its parent (ie the componentStyleMap)

    • Similarly, maybe if a block has an explicit style set, it shouldn't be able to inherit from anything
  • user-defined style properties

    • parameterized and combinable/overridable
  • Finish MultiSelect (currently may not fire certain events with certain ways of selecting things with the mouse)

  • Make all controls usable via the keybaord

    • eg. checkboxes should be toggled if you press enter while they're focused on
  • Consider making Style objects dynamically changable, and also inheritable/extendable so that you can extend the style object of a Block instead of having to extend the object passed to a Style prototype

  • in separate module (a Blocks utility kit or something):

    • RadioSet (a set of labeled radio buttons)
    • TextEditor

Optimization ideas:

  • When possible, use a WeakMap to cache Style mixes, componentStyleMap conjunctions, etc so that extraneous style don't cause memory leaks
  • When dom nodes are added, either add them inside a setTimeout, or render their styles in a setTimeout (first way's probably best so you have less change of seeing unstyled blocks)
    • This should improve UI responsiveness, but not execution time
  • Purge style cache entries after a certain age (for non-weak maps)
  • Use document fragments when adding multiple dom nodes
  • Mix together defaultStyles statically (once per block type) since they're not dynamic
  • 1.1.9 - Making Selects and Options able to have non-string values
  • 1.1.8 - fixing broken style caching (by removing a cache step)
  • 1.1.7
    • Attempting to fix a bug caused by a cache that wasn't specific enough, triggered by native pseudoclass interacting with non-native styles
    • Allowing style definitions (rather than Style objects) to be passed into Style.mix
  • 1.1.6 - Another native pseudoclass bug fix related to overrides of other pseudoclasseses
  • 1.1.5 - Another native pseudoclass bug fix related to overrides
  • 1.1.4 - Fixing bug where base defaults weren't being used for native-rendered pseudoclass styles in cases where a block doesn't have a defaultStyle
  • 1.1.3 - fixing bug in TextField, and optimizing Style performance by only creating each css class once (was creating once per block)
  • 1.1.2
    • fixing minor bug where in certain cases involving native-rendered pseudoclass styles, the browser's default value was used instead of blocks's default
    • Attempting to improve style cache performance
    • MINOR BREAKING CHANGE: detach can no longer take an optional first parameter, but always detaches blocks from whatever dom parent they have
    • Fixing bugs in attach and detach
    • Speeding up the addAt method and .style setter by between 10 and 30 times by
      • only rendering styles once the blocks are attached to the document and
      • fixing a couple bugs that were causing cached style not to be used
    • Changing the block.attach method and Blocks.attach function to take an optional first parameter - a domNode to append to in place of document.body
      • MINOR BREAKING CHANGE 1: the Blocks.attach function can no longer take varargs of blocks (eg Blocks.attach(block1, block2, block2) - instead do Blocks.attach([block1, block2, block2]))
    • Fixing bug: native pseudoclass style overriding block default styles when they must override a StyleMap style with "initial"
    • MINOR BREAKING CHANGE 2: It is now required that a block be attached to the document with the attach function or method. Without this, styles won't be rendered.
  • 1.0.3 - fixing native pseudo element rendering
  • 1.0.2 - making processParameter in addPseudoClass optional like the docs say
  • 1.0.1
      * Adding the $inherit style property
      * Optimizing the style adding code a little
  • 1.0.0
      * Major Style object refactor
      * Fixing various pseudoclass bugs where pseudoclasses weren't working in dynamic situations, emulated pseudoclass setup function being called twice, and metapseudoclasses like :not weren't working
      * Pseudoclasses can now be styled with full `Style` objects (that use any Style feature)
      * Optimizing pseudoclass styles when their style branch can be rendered in pure-css
      * `defaultStyle` styles can be arbitrary Style objects now
      * $state styles can be arbitrary Style objects now
      * $label changed from being a modifier on a Block style to indicating a whole new labeled block style (see section on $label for details)
      * augmenting nth-child to be able to be more sane in how it processes its input (you can reverse the order of the terms and whitespace is tolerated)
      * changing the default of box-sizing to 'border-box' except for images, which retain the 'content-box' default
  • 0.9.17 - requiring a node to be removed from its parent before its added to a different parent
  • 0.9.16 - fixing text for
  • 0.9.15
      * if `undefined` is passed as a style, it is now ignored
      * fixing bug: an array of blocks couldn't be passed to `table.cell`
  • 0.9.14 - Improving fix for when blocks.js is loaded twice (seemed to fix an additional problem i saw where defaults were sometimes overriding styles from other instances of blocks.js, possibly related to load order of scripts? Unfortunately I couldn't create a test to repro)
  • 0.9.13
      * Fixing issue where styles break if block.js is loaded twice (also adding a warning when it detects two instances of blocks.js)
      * Adding a little more documentation around $state
  • 0.9.12
      * bringing back the $state style in a slightly different form
      * fixing a bug in label argument interpretation
      * getting rid of npm-shrinkwrap and fixing up dependency versioning to be generally lenient but strict on major version
  • 0.9.11 - updating hashmap version, since it was giving me trouble in another project
  • 0.9.10
      * remove the $state style thing - $setup and $kill cover it
      * allow $setup to return a value that's then passed to $kill (so they aren't forced to set properties on the block)
  • 0.9.9 adding better require paths for commonjs
  • 0.9.8 - writing all this documentation
  • 0.9.7 - Added List, Image, and Canvas
  • 0.9.6 - Fixed but in EventEmitterB that was causing catch-all ifon handlers to not fire on-call if events were already attached beforehand
  • 0.9.5
      * Used default stying to set defaults on some of the built in Blocks
      * Fixed a bug in ifon when its called without an event and there are already events set up
  • 0.9.4 - Create a way to set unobtrusive default styles for custom Blocks (so you can, for example, make Option blocks display: block)
  • 0.9.3 - Support styling blocks via their inheritance tree (ie if A inherits from B, styling A should style A and B, but a B style should override an A style)
  • 0.9.2
      * Using `ifon` and `ifoff` for proxying browser events through Blocks
      * Override the `on` method so that standard browser events are automatically attached to domNodes
          * provide a way to exclude certain events, so they can be set up in an alternate way
  • 0.9.1
      * Adding tests for all the public Block properties that didn't already have tests
      * Changing API of focus/blur, show/hide, and selection methods to getter/setter style properties
      * Replacing getCaretPosition to selectionRange that returns the full selection range
      * Made the selection stuff work for inputs and text areas
      * Adding `ifon` and `ifoff` methods
  • 0.1.1 - Creating a bunch of conventions that all the standard blocks conform to
  • 0.1.0 - Initial commit - code transferred from private project.
How to Contribute!

Want to contribute? Start with the Contributing Guide!

Anything helps:

  • Creating issues (aka tickets/bugs/etc). Please feel free to use issues to report bugs, request features, and discuss changes.
  • Updating the documentation: ie this readme file. Be bold! Help create great documentation!
  • Submitting pull requests.

Released under the MIT license: