$digest: function() {var watch, value, last,watchers,asyncQueue = this.$$asyncQueue,postDigestQueue = this.$$postDigestQueue,length,dirty, ttl = TTL,next, current, target = this,watchLog = [],logIdx, logMsg, asyncTask;//beginPhase和clearPhase 用来进行状态管理beginPhase('$digest');lastDirtyWatch = null;do { // "while dirty" loopdirty = false;current = target;while(asyncQueue.length) {try {asyncTask = asyncQueue.shift();asyncTask.scope.$eval(asyncTask.expression);} catch (e) {clearPhase();$exceptionHandler(e);}lastDirtyWatch = null;}traverseScopesLoop:do { // "traverse the scopes" loopif ((watchers = current.$$watchers)) {// process our watcheslength = watchers.length;while (length--) {try {watch = watchers[length];// Most common watches are on primitives, in which case we can short// circuit it with === operator, only when === fails do we use .equalsif (watch) {if ((value = watch.get(current)) !== (last = watch.last) &&!(watch.eq? equals(value, last): (typeof value == 'number' && typeof last == 'number'&& isNaN(value) && isNaN(last)))) {dirty = true;lastDirtyWatch = watch;watch.last = watch.eq ? copy(value) : value;watch.fn(value, ((last === initWatchVal) ? value : last), current);if (ttl < 5) {logIdx = 4 - ttl;if (!watchLog[logIdx]) watchLog[logIdx] = [];logMsg = (isFunction(watch.exp))? 'fn: ' + (watch.exp.name || watch.exp.toString()): watch.exp;logMsg += '; newVal: ' + toJson(value) + '; oldVal: ' + toJson(last);watchLog[logIdx].push(logMsg);}} else if (watch === lastDirtyWatch) {// If the most recently dirty watcher is now clean, short circuit since the remaining watchers// have already been tested.dirty = false;break traverseScopesLoop;}}} catch (e) {clearPhase();$exceptionHandler(e);}}}// Insanity Warning: scope depth-first traversal// yes, this code is a bit crazy, but it works and we have tests to prove it!// this piece should be kept in sync with the traversal in $broadcastif (!(next = (current.$$childHead ||(current !== target && current.$$nextSibling)))) {while(current !== target && !(next = current.$$nextSibling)) {current = current.$parent;}}} while ((current = next));// `break traverseScopesLoop;` takes us to hereif((dirty || asyncQueue.length) && !(ttl--)) {clearPhase();throw $rootScopeMinErr('infdig','{0} $digest() iterations reached. Aborting!\n' +'Watchers fired in the last 5 iterations: {1}',TTL, toJson(watchLog));}} while (dirty || asyncQueue.length);clearPhase();while(postDigestQueue.length) {try {postDigestQueue.shift()();} catch (e) {$exceptionHandler(e);}}},$destroy: function() {// we can't destroy the root scope or a scope that has been already destroyedif (this.$$destroyed) return;var parent = this.$parent;this.$broadcast('$destroy');this.$$destroyed = true;if (this === $rootScope) return;forEach(this.$$listenerCount, bind(null, decrementListenerCount, this));if (parent.$$childHead == this) parent.$$childHead = this.$$nextSibling;if (parent.$$childTail == this) parent.$$childTail = this.$$prevSibling;if (this.$$prevSibling) this.$$prevSibling.$$nextSibling = this.$$nextSibling;if (this.$$nextSibling) this.$$nextSibling.$$prevSibling = this.$$prevSibling;// This is bogus code that works around Chrome's GC leak// see: https://github.com/angular/angular.js/issues/1313#issuecomment-10378451this.$parent = this.$$nextSibling = this.$$prevSibling = this.$$childHead =this.$$childTail = null;},$eval: function(expr, locals) {return $parse(expr)(this, locals);},$evalAsync: function(expr) {// if we are outside of an $digest loop and this is the first time we are scheduling async// task also schedule async auto-flushif (!$rootScope.$$phase && !$rootScope.$$asyncQueue.length) {//$browser.defer 把这个看做setTimout$browser.defer(function() {if ($rootScope.$$asyncQueue.length) {$rootScope.$digest();}});}this.$$asyncQueue.push({scope: this, expression: expr});},$$postDigest : function(fn) {this.$$postDigestQueue.push(fn);},//执行完expr，会$digest一遍。//这样做得好处是，expr的执行不会影响到$digest$apply: function(expr) {try {beginPhase('$apply');return this.$eval(expr);} catch (e) {$exceptionHandler(e);} finally {clearPhase();try {$rootScope.$digest();} catch (e) {$exceptionHandler(e);throw e;}}},//$broadcast,$on,$emit 省略掉//$broadcast,$emit 的作用就是，沿着Scope的关系上下注册的事件,事件的格式要注意一下//{//          name: name,//          targetScope: scope,//          stopPropagation: function() {stopPropagation = true;},//          preventDefault: function() {//            event.defaultPrevented = true;//          },//          defaultPrevented: false//        },这些可以用来阻止事件的冒泡//$on的事件存储在每个$scope中的 $$listeners对象中，可以多次$on同一个namevar $rootScope = new Scope();return $rootScope;//类似于java中的线程锁的概念function beginPhase(phase) {if ($rootScope.$$phase) {throw $rootScopeMinErr('inprog', '{0} already in progress', $rootScope.$$phase);}$rootScope.$$phase = phase;}function clearPhase() {$rootScope.$$phase = null;}}

看到这里，可以看出angularJS以响应status变化的模式（具体的学术性名称忘掉了）来做监控，在js中，这会导致随着status的增多，监控会越来越慢的问题。或许在js中，也只能如此的做监控了。如果读者知道有做js函数式响应监控的框架或demo，麻烦留言一下。嘿嘿。