js对象的复制继承实例

<script type="text/javascript">
Object.prototype.extend = function(obj){
 //在函数里，把obj属性复制到自身
 for(var k in obj){
  if(obj.hasOwnProperty(k)){
   if(this[k] == undefined){
    this[k] = obj[k];
   }
  }
 }
}
var kitty = {color:'yellow',climb:function(){alert('我会爬树');}};
var tiger = {color:'yellow and black'};
tiger.extend(kitty);
tiger.climb();
</script>