订阅功能的部分实现代码如下：
/* ?*/var uid = 0;/** * A dep is an observable that can have multiple * directives subscribing to it. */var Dep = function Dep () { ?this.id = uid++; ?this.subs = [];};Dep.prototype.addSub = function addSub (sub) { ?this.subs.push(sub);};Dep.prototype.removeSub = function removeSub (sub) { ?remove(this.subs, sub);};Dep.prototype.depend = function depend () { ?if (Dep.target) { ???Dep.target.addDep(this); ?}};Dep.prototype.notify = function notify () { ?// stabilize the subscriber list first ?var subs = this.subs.slice(); ?for (var i = 0, l = subs.length; i < l; i++) { ???subs[i].update(); ?}};// the current target watcher being evaluated.// this is globally unique because there could be only one// watcher being evaluated at any time.Dep.target = null;var targetStack = [];function pushTarget (_target) { ?if (Dep.target) { targetStack.push(Dep.target); } ?Dep.target = _target;}function popTarget () { ?Dep.target = targetStack.pop();}/* ?*/vuejs源码摘抄
原文地址：http://www.cnblogs.com/aliwa/p/7767459.html