什么是filelist，Lazy-evaluating list of files, based on globs or regex patterns
A FileList is a lazy-evaluated list of files. When given a list of glob patterns for possible files to be included in the file list, instead of searching the file structures to find the files, a FileList holds the pattern for latter use.
This allows you to define a FileList to match any number of files, but only search out the actual files when then FileList itself is actually used. The key is that the first time an element of the FileList/Array is requested, the pending patterns are resolved into a real list of file names.
Add files to the list with the
include method. You can add glob patterns, individual files, or RegExp objects. When the Array methods are invoked on the FileList, these items are resolved to an actual list of files.
var fl = new FileList(); fl.include('test/*.js'); fl.exclude('test/helpers.js');
exclude method to override inclusions. You can use this when your inclusions are too broad.
FileList has lazy-evaluated versions of most of the array methods, including the following:
When you call one of these methods, the items in the FileList will be resolved to the full list of files, and the method will be invoked on that result.
length: FileList includes a length method (instead of a property) which returns the number of actual files in the list once it’s been resolved.
include: Add a filename/glob/regex to the list
exclude: Override inclusions by excluding a filename/glob/regex
resolve: Resolve the items in the FileList to the full list of files. This method is invoked automatically when one of the array methods is called.
toArray: Immediately resolves the list of items, and returns an actual array of filepaths.
clearInclusions: Clears any pending items – must be used before resolving the list.
clearExclusions: Clears the list of exclusions rules.