20+行代码使用es5 Object.defineProperty 实现简单的watch功能

/**
* 一个简单的demo 帮助理解defineProperty,只对Object类型参数有效
*/
$watch=function(myObject,callback){
function initWatch(obj){
for(var i in obj){
if(typeof obj!='object'){
return;
}
(function(value,o,attr){
var v=value;
var oldValue=value;
Object.defineProperty(o,attr,{
get:function(){
return v;
},
set:function (newValue){
oldValue=v;
v=newValue;
callback(newValue,oldValue)
}
});
})(obj[i],obj,i);
initWatch(obj[i]);
}
}
initWatch(myObject);
};
var a={
name:'Lee',
background:{
hometown:'De Zhou',
presentAddr:'Texas'
}
}
$watch(a,function(newValue,oldValue){
console.log(a.name+" moved from "+ oldValue + " to " + newValue);
})
a.background.presentAddr="New York"
//Lee moved from Texas to New York
//"New York"