javascript 用函数实现继承详解

<script type="text/javascript"> 
  var child={}; 
  var mother={ 
    name:"zhangzhiying", 
    lastAge:21, 
    sex:"女"
  }; 
  function extend(target,source){ 
  　　　　for(var p in source){ 
    　　target[p]=source[p]; 
  　　　　} 
  　　　　return target; 
  } 
  extend(child,mother); 
  console.log(child);   //<STRONG>Object {name: "zhangzhiying", lastAge: 21, sex: "女"}</STRONG> 
</script> 

<script type="text/javascript"> 
  var child={}; 
  var mother={ 
    name:"zhangzhiying", 
    lastAge:21, 
    <STRONG>set age(value){ 
      this.lastAge=value; 
    }, 
    get age(){ 
      return this.lastAge+1; 
    },</STRONG> 
    sex:"女"
  };<BR>　　　　<STRONG>　mother.age=15;</STRONG>    //有set方法，具有可写性 
  function extend(target,source){ 
  　　　　for(var p in source){ 
    　　target[p]=source[p]; 
  　　　　} 
  　　　　return target; 
  } 
  extend(child,mother); 
  console.log(child);  //<STRONG>Object {name: "zhangzhiying", lastAge: 15, age: 16, sex: "女"}</STRONG> 
</script>

<script type="text/javascript"> 
  var child={}; 
  var mother={ 
    name:"zhangzhiying", 
    lastAge:21, 
    set age(value){ 
      this.lastAge=value; 
    }, 
    get age(){ 
      return this.lastAge+1; 
    }, 
    sex:"女"
  }; 
  Object.defineProperty(mother,"lastAge",{writable:false}); //把lastAge设置成了不可写 
  mother.age=15;                       //设置无效，因为lastAge的值不变，所以lastAge+1不变，即age不变 
  function extend(target,source){ 
    for(var p in source){ 
    target[p]=source[p]; 
  } 
  return target; 
  } 
  extend(child,mother); 
  console.log(child);   //Object {name: "zhangzhiying", lastAge: 21, age: 22, sex: "女"} 
  child.lastAge=12;　　　　//结果显示lastAge改变，说明child.lastAge没有“继承”到mother.lastAge的特性，我们再用getOwnPropertyDesriptor()方法确认一下<BR>　　　　 console.log(Object.getO

<EM id=__mceDel></script> 
</EM> 

<script type="text/javascript"> 
  var child={}; 
  var mother={ 
    name:"zhangzhiying", 
    lastAge:21, 
    set age(value){ 
      this.lastAge=value; 
    }, 
    get age(){ 
      return this.lastAge+1; 
    }, 
    sex:"女"
  }; 
  Object.defineProperty(mother,"lastAge",{writable:false}); 
  mother.age=15; 
  <SPAN style="COLOR: #333399"><STRONG>function extend(target,source){ 
    var names=Object.getOwnPropertyNames(source);  //获取所有的属性名 
    for(var i=0;i<names.length;i++){ 
      if(names[i] in target) continue;  //如果这个属性存在，就跳过（原型继承中，如果自有属性和原型对象的属性重名，保留自有属性） 
      var desc=Object.getOwnPropertyDescriptor(source,names[i]);  //获取mother属性的描述符对象（即属性特性的集合，es5中用描述符对象来表示） 
      Object.defineProperty(target,names[i],desc);  //将mother的描述符对象给child的属性定义 
    } 
    return target; 
  }</STRONG></SPAN> 
  extend(child,mother); 
  console.log(child); 
  child.lastAge=12; 
  console.log(Object.getOwnPropertyDescriptor(child,"lastAge")); 
  console.log(child); 
</script>