剩下一个watch模块，这个模块比较深，先大概过一下整体涉及内容再分部讲解。
流程图如下：
NodeWatchFileSystem
const Watchpack = require("watchpack");class NodeWatchFileSystem {constructor(inputFileSystem) {this.inputFileSystem = inputFileSystem;this.watcherOptions = {aggregateTimeout: 0};this.watcher = new Watchpack(this.watcherOptions);}watch(files, /*Array*/dirs, /*Array*/missing, /*Array*/startTime, /*number*/options, /*object*/callback, /*function*/callbackUndelayed /*function*/) {// params validate...const oldWatcher = this.watcher;// 生成Watchpack对象this.watcher = new Watchpack(options);if (callbackUndelayed)this.watcher.once("change", callbackUndelayed);this.watcher.once("aggregated", (changes, removals) => { /**/ });// 调用watch方法this.watcher.watch(files.concat(missing), dirs.concat(missing), startTime);if (oldWatcher) {oldWatcher.close();}return {close: () => { /**/ },pause: () => { /**/ }};}
}module.exports = NodeWatchFileSystem; 除去细节代码，该模块大体如下；
1、引入Watchpack模块
2、接受一个inputFileSystem作为构造函数的参数
3、根据配置选项实例化一个Watchpack类
4、核心watch方法为调用实例类的watch方法，传入给定参数，绑定两个一次性事件绑定并返回了一个对象
模块核心的方法调用的是Watchpack实体类上的，所以需要进一步探究该类。
该模块涉及到了nodejs的event模块，内容非常简单，这里就不做介绍了，详情可查看官网API:https://nodejs.org/dist/latest-v8.x/docs/api/events.html
Watchpack
var watcherManager = require("./watcherManager"); var EventEmitter = require("events").EventEmitter; Watchpack.prototype = Object.create(EventEmitter.prototype);class Watchpack {constructor(options) {EventEmitter.call(this);if (!options) options = {};if (!options.aggregateTimeout) options.aggregateTimeout = 200;this.options = options;this.watcherOptions = {ignored: options.ignored,poll: options.poll};this.fileWatchers = [];this.dirWatchers = [];this.mtimes = Object.create(null);this.paused = false;this.aggregatedChanges = [];this.aggregatedRemovals = [];this.aggregateTimeout = 0;this._onTimeout = this._onTimeout.bind(this);}watch(files, directories, startTime) {this.paused = false;var oldFileWatchers = this.fileWatchers;var oldDirWatchers = this.dirWatchers;this.fileWatchers = files.map(function(file) {return this._fileWatcher(file, watcherManager.watchFile(file, this.watcherOptions, startTime));}, this);this.dirWatchers = directories.map(function(dir) {return this._dirWatcher(dir, watcherManager.watchDirectory(dir, this.watcherOptions, startTime));}, this);oldFileWatchers.forEach(function(w) {w.close();}, this);oldDirWatchers.forEach(function(w) {w.close();}, this);};pause() { /**/ };getTimes() { /**/ };_fileWatcher(file, watcher) { /**/ };_dirWatcher(item, watcher) { /**/ };_onChange(item, mtime, file) { /**/ };_onRemove(item, file) { /**/ };_onTimeout() { /**/ };close() { /**/ }; }module.exports = Watchpack;function addWatchersToArray(watchers, array) { /**/ }
本模块引入了并继承了nodejs的EventEmitter，并引入了新模块watcherManager，主要内容罗列如下：
1、构造函数接受一个对象，键包括aggregateTimeout、ignored、poll，本例只传入第一个并设置为0
2、核心方法为watch，依赖于引入的watchManager模块
3、其余方法均为工具方法
WatcherManager
var path = require("path");class WatcherManager {constructor() {this.directoryWatchers = {};};// 工厂函数 getDirectoryWatcher(directory, options) {// 引入模块var DirectoryWatcher = require("./DirectoryWatcher");options = options || {};var key = directory + " " + JSON.stringify(options);if (!this.directoryWatchers[key]) {this.directoryWatchers[key] = new DirectoryWatcher(directory, options);// 文件监视结束则从容器删除this.directoryWatchers[key].on("closed", function() {delete this.directoryWatchers[key];}.bind(this));}return this.directoryWatchers[key];};// 监视文件 watchFile(p, options, startTime) {var directory = path.dirname(p);return this.getDirectoryWatcher(directory, options).watch(p, startTime);};// 监视目录 watchDirectory(directory, options, startTime) {return this.getDirectoryWatcher(directory, options).watch(directory, startTime);}; } module.exports = new WatcherManager();
可以看出这是一个中间处理函数，其中构造函数生成了一个容器，容器的键为目录+参数生成的一个字符串，当监视关闭后会并立即删除。
这个模块类似于tapable，是一个监视对象管理器。
然后是监视核心实现模块，模块内容比较多，这里只简单看一下构造函数以及watch方法：
var EventEmitter = require("events").EventEmitter; var async = require("async"); var chokidar = require("chokidar"); var fs = require("graceful-fs");class Watcher {constructor(directoryWatcher, filePath, startTime) {EventEmitter.call(this);this.directoryWatcher = directoryWatcher;this.path = filePath;this.startTime = startTime && +startTime;this.data = 0;};checkStartTime(mtime, initial) { /**/ };close() { /**/ }; }function DirectoryWatcher(directoryPath, options) {EventEmitter.call(this);this.options = options;this.path = directoryPath;this.files = Object.create(null);this.directories = Object.create(null);this.watcher = chokidar.watch(directoryPath, {ignoreInitial: true,persistent: true,followSymlinks: false,depth: 0,atomic: false,alwaysStat: true,ignorePermissionErrors: true,ignored: options.ignored,usePolling: options.poll ? true : undefined,interval: typeof options.poll === "number" ? options.poll : undefined,disableGlobbing: true});this.watcher.on("add", this.onFileAdded.bind(this));this.watcher.on("addDir", this.onDirectoryAdded.bind(this));this.watcher.on("change", this.onChange.bind(this));this.watcher.on("unlink", this.onFileUnlinked.bind(this));this.watcher.on("unlinkDir", this.onDirectoryUnlinked.bind(this));this.watcher.on("error", this.onWatcherError.bind(this));// ... }DirectoryWatcher.prototype.watch = function watch(filePath, startTime) {this.watchers[withoutCase(filePath)] = this.watchers[withoutCase(filePath)] || [];this.refs++;var watcher = new Watcher(this, filePath, startTime);watcher.on("closed", function() { /**/ }.bind(this));// ...return watcher; };// ... module.exports = DirectoryWatcher;
从构造函数和模块引入可以得到很多信息，如下：
1、引入了graceful-js模块，可以看出底层还是利用nodejs的fs模块来进行监视
2、所有的监视事件都是基于nodejs的EventEmitter模块来进行操作
3、内部还有一个辅助类Watcher
4、根据构造函数的代码，监视的操作包含(可能不限于)新增文件、新增文件夹、改变内容、删除文件、删除文件夹等
async模块是一个类似于tapable的辅助工具，用于异步处理批量方法，详细内容可自行去网上查阅。
构造函数中，该模块又再次引用了chokidar模块，并调用其watch方法进行初始化，看似调用方法，源码简化后如下：
class FSWatcher {// ... } exports.FSWatcher = FSWatcher; exports.watch = function(paths, options) {return new FSWatcher(options).add(paths); };
假的，这还是个new操作，只是为了方便把两步合成到了一个方法中。
所有的模块整理如上，下面几节再来剖析每一块内容。
