knockout.js的学习笔记4

本节对第三节的代码进行重构一下。

我们发现$.computed其实也是一种$.observable，因此可以写成这样：

var validValueType = $.oneObject("Null,NaN,Undefined,Boolean,Number,String")
$.dependencyChain = (function () {
var _frames = [];
return {
begin: function (ret) {
_frames.push(ret);
},
end: function () {
_frames.pop();
},
collect: function (self) {
if (_frames.length > 0) {
self.list = self.list || [];
var fn = _frames[_frames.length - 1];
if ( self.list.indexOf( fn ) >= 0)
return;
self.list.push(fn);
}
}
};
})();
$.notifyUpdate = function(observable){
var list = observable.list
if($.type(list,"Array")){
for(var i = 0, el; el = list[i++];){
el();//通知顶层的computed更新自身
}
}
}
$.computed = function(obj, scope){
var args//构建一个至少拥有getter,scope属性的对象
if(typeof obj == "function"){
args = {
getter: obj,
scope: scope
}
}else if( typeof obj == "object" && obj && obj.getter){
args = obj
}
return $.observable(args, true)
}

$.observable = function(old, isComputed){
var cur, getter, setter, scope
function ret(neo){
var set;//判定是读方法还是写方法
if(arguments.length){ //setter
neo =  typeof setter === "function" ? setter.call( scope, neo ) : neo
set = true;
}else{  //getter
if(typeof getter === "function"){
$.dependencyChain.begin(ret);//只有computed才在依赖链中暴露自身
neo = getter.call( scope )
console.log(neo+"!!!!!!!!!!")//用来查看执行情况
$.dependencyChain.end()
}else{
neo = cur
}
$.dependencyChain.collect(ret)//将暴露到依赖链的computed放到自己的通知列表中
}
if(cur !== neo ){
cur = neo;
$.notifyUpdate(ret)
}
return set ? ret : cur
}
if( isComputed == true){
getter = old.getter;  setter = old.setter; scope  = old.scope;
ret();//必须先执行一次
}else{
old = validValueType[$.type(old)] ? old : void 0;
cur = old;//将上一次的传参保存到cur中,ret与它构成闭包
ret(old);//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);
this.wordcard = $.computed(function(){
return this.card() +"工作卡 "
},this)
this.wordcardA = $.computed(function(){
return this.wordcard() +"A "
},this)
}

window.onload = function(){
var model = new MyViewModel();

$.log("==================")
model.lastName("last");
$.log("==================")

}

打印如下：

Planet Earth 屌丝!!!!!!!!!!
Planet Earth 屌丝工作卡 !!!!!!!!!!
Planet Earth!!!!!!!!!!
Planet Earth 屌丝!!!!!!!!!!
Planet Earth 屌丝工作卡 !!!!!!!!!!
Planet Earth 屌丝工作卡 A !!!!!!!!!!
==================
Planet last!!!!!!!!!!
Planet last!!!!!!!!!!
Planet last 屌丝!!!!!!!!!!
Planet last!!!!!!!!!!
Planet last 屌丝!!!!!!!!!!
Planet last 屌丝工作卡 !!!!!!!!!!
Planet last!!!!!!!!!!
Planet last 屌丝!!!!!!!!!!
Planet last 屌丝工作卡 !!!!!!!!!!
Planet last 屌丝工作卡 A !!!!!!!!!!
==================

依赖链发生效力了！不过感觉糟极了，有许多通知是没必要的。我们在$.notifyUpdate与$.observable添加缓存机制看看：

$.notifyUpdate = function(observable){
var list = observable.list;
if($.type(list,"Array")){
for(var i = 0, el; el = list[i++];){
delete el.cache;//清除缓存
el();//通知顶层的computed更新自身
}
}
}
//**********************略***************
$.observable = function(old, isComputed){
//**********************略***************
function ret(neo){
var set;//判定是读方法还是写方法
if(arguments.length){ //setter
neo =  typeof setter === "function" ? setter.apply( scope, arguments ) : neo
set = true;
}else{  //getter
if(typeof getter === "function"){
$.dependencyChain.begin(ret);//只有computed才在依赖链中暴露自身
if("cache" in ret){
neo = ret.cache;//从缓存中读取,防止递归
}else{
neo = getter.call( scope );
ret.cache = neo;//保存到缓存
console.log(neo+"!!!!!!!!!!");//
}
$.dependencyChain.end()
}else{
neo = cur
}
$.dependencyChain.collect(ret)//将暴露到依赖链的computed放到自己的通知列表中
}
if(cur !== neo ){
cur = neo;
$.notifyUpdate(ret);
}
return set ? ret : cur
}
//**********************略***************
if( isComputed == true){
getter = old.getter;  setter = old.setter; scope  = old.scope;
ret();//必须先执行一次
}else{
old = validValueType[$.type(old)] ? old : void 0;
cur = old;//将上一次的传参保存到cur中,ret与它构成闭包
ret(old);//必须先执行一次
}
return ret
}

这时它的情况就好多了：

Planet
Earth
Planet Earth!!!!!!!!!!
Planet Earth 屌丝!!!!!!!!!!
Planet Earth 屌丝工作卡 !!!!!!!!!!
Planet Earth 屌丝工作卡 A !!!!!!!!!!
==================
Planet last!!!!!!!!!!
Planet last 屌丝!!!!!!!!!!
Planet last 屌丝工作卡 !!!!!!!!!!
Planet last 屌丝工作卡 A !!!!!!!!!!
==================