本节换一种方式解读，把我消化过的东西反刍出来可能这样大家容易理解些，knockout.js大量使用闭包，非常难读。
我们从viewModel看起：
function MyViewModel() { this.firstName = $.observable('Planet'); this.lastName = $.observable('Earth'); this.fullName = $.computed({ getter: function () { return this.firstName() + " " + this.lastName(); }, setter: function (value) { var lastSpacePos = value.lastIndexOf(" "); if (lastSpacePos > 0) { // Ignore values with no space character this.firstName(value.substring(0, lastSpacePos)); // Update "firstName" this.lastName(value.substring(lastSpacePos + 1)); // Update "lastName" } }, scope: this }); } var a = new MyViewModel(); a.fullName("xxx yyy") 这里包含两种observable，没有依赖的与有依赖的，有依赖的通过没有依赖的计算出来，因此叫做computed！
但不管怎么样，它们都是返回一个函数，我们通过如下代码就可以模拟它们了：
//注：这里会用到mass Framework的种子模块的API https://github.com/RubyLouvre/mass-Framework/blob/master/src/mass.js //observable的传参必须是基本类型 var validValueType = $.oneObject("Null,NaN,Undefined,Boolean,Number,String"); $.observable = function(value){ var v = value;//将上一次的传参保存到v中,ret与它构成闭包 function ret(neo){ if(arguments.length){ //setter if(!validValueType[$.type(neo)]){ $.error("arguments must be primitive type!") return ret } if(v !== neo ){ v = neo; } return ret; }else{ //getter return v; } } value = validValueType[$.type(value)] ? value : void 0; ret(arguments[0]);//必须先执行一次 return ret } $.computed = function(obj, scope){//为一个惰性函数，会重写自身 //computed是由多个$.observable组成 var getter, setter if(typeof obj == "function"){ getter = obj }else if(obj && typeof obj == "object"){ getter = obj.getter; setter = obj.setter; scope = obj.scope; } var v var ret = function(neo){ if(arguments.length ){ if(typeof setter == "function"){//setter不一定存在的 if(!validValueType[$.type(neo)]){ $.error("arguments must be primitive type!") return ret } if(v !== neo ){ setter.call(scope, neo); v = neo; } } return ret; }else{ v = getter.call(scope); return v; } } ret(); //必须先执行一次 return ret; } 因此当我们执行new MyViewModel(),就会依次执行$.observable, $.observable, $.computed, $.computed中的参数的getter, getter再调用两个observable。
问题来了，当我们调用computed时，总会通知其依赖（即firstName ，lastName）进行更新，但firstName 发生改变时没有手段通知fullName 进行更新。ko把这逻辑写在dependencyDetection模块中。我简化如下：
$.dependencyDetection = (function () { var _frames = []; return { begin: function (ret) { _frames.push(ret); }, end: function () { _frames.pop(); }, collect: function (self) { if (_frames.length > 0) { if(!self.list) self.list = []; var fn = _frames[_frames.length - 1]; if ( self.list.indexOf( fn ) >= 0) return; self.list.push(fn); } } }; })(); 我们把它加入到 $.computed 与 $.observable中，再添加一个发布更新函数valueWillMutate
var validValueType = $.oneObject("Null,NaN,Undefined,Boolean,Number,String") $.dependencyDetection = (function () { var _frames = []; return { begin: function (ret) { _frames.push(ret); }, end: function () { _frames.pop(); }, collect: function (self) { if (_frames.length > 0) { if(!self.list) self.list = []; var fn = _frames[_frames.length - 1]; if ( self.list.indexOf( fn ) >= 0) return; self.list.push(fn); } } }; })(); $.valueWillMutate = function(observable){ var list = observable.list if($.type(list,"Array")){ for(var i = 0, el; el = list[i++];){ el(); } } } $.observable = function(value){ var v = value;//将上一次的传参保存到v中,ret与它构成闭包 function ret(neo){ if(arguments.length){ //setter if(!validValueType[$.type(neo)]){ $.error("arguments must be primitive type!") return ret } if(v !== neo ){ v = neo; $.valueWillMutate(ret);//向依赖者发送通知 } return ret; }else{ //getter $.dependencyDetection.collect(ret);//收集被依赖者 return v; } } value = validValueType[$.type(value)] ? value : void 0; ret(arguments[0]);//必须先执行一次 return ret } $.computed = function(obj, scope){//为一个惰性函数，会重写自身 //computed是由多个$.observable组成 var getter, setter if(typeof obj == "function"){ getter = obj }else if(obj && typeof obj == "object"){ getter = obj.getter; setter = obj.setter; scope = obj.scope; } var v var ret = function(neo){ if(arguments.length ){ if(typeof setter == "function"){//setter不一定存在的 if(!validValueType[$.type(neo)]){ $.error("arguments must be primitive type!") return ret } if(v !== neo ){ setter.call(scope, neo); v = neo; } } return ret; }else{ $.dependencyDetection.begin(ret);//让其依赖知道自己的存在 v = getter.call(scope); $.dependencyDetection.end(); return v; } } ret(); //必须先执行一次 return ret; } function MyViewModel() { this.firstName = $.observable('Planet'); this.lastName = $.observable('Earth'); this.fullName = $.computed({ getter: function () { return this.firstName() + " " + this.lastName(); }, setter: function (value) { var lastSpacePos = value.lastIndexOf(" "); if (lastSpacePos > 0) { // Ignore values with no space character this.firstName(value.substring(0, lastSpacePos)); // Update "firstName" this.lastName(value.substring(lastSpacePos + 1)); // Update "lastName" } }, scope: this }); this.card = $.computed(function(){ return this.fullName() +" 屌丝" },this) } var a = new MyViewModel(); //============测试代码============ $.log(a.firstName())//Planet $.log(a.lastName())//Earth $.log(a.fullName())//Planet Earth 通过上面两个计算出来 a.fullName("xxx yyy");//更新fullName会自动更新firstName与lastName $.log(a.firstName())//xxx $.log(a.lastName())//yyy a.firstName("ooo");//更新firstName会自动更新fullName $.log(a.fullName())//ooo yyy $.log(a.card())//ooo yyy 屌丝 到这里viewModel中的每个域（firstName, lastName, fullName）只要存在依赖关系都能相互通知了。