ExtJs关于Ext.extend()的说明

Ext.extend方法是用来实现类的继承。
extend(Object subclass,Object superclass,[Object overrides] : Object
第一个参数：子类
第二个参数：父类
第三个参数：要覆盖的属性。
这里需要强调一下，子类继承下来的是父类中通过superclass.prototype方式定义的属性（包括用此方法定义的函数）。
例子如下：

Js代码

1. <script type="text/javascript">   
2.             function S(){   
3.              }   
4.              S.prototype.s = "s";   
5.              S.prototype.s1 = "s1";   
6.             function C(){   
7.                 this.c = "c";   
8.                 this.c1 = "c1";   
9.              }   
10.              Ext.extend(C,S,{s1:"by c overload"});   
11.             var c = new C();   
12.              alert(c.s); //s   
13.              alert(c.s1); //by c overload   
14.          </script>  

<script type="text/javascript">   function S(){   }   S.prototype.s = "s";   S.prototype.s1 = "s1";   function C(){    this.c = "c";    this.c1 = "c1";   }   Ext.extend(C,S,{s1:"by c overload"});   var c = new C();   alert(c.s); //s   alert(c.s1); //by c overload  </script>

如果按下面这个方式写就会提示c.s没有定义(undefind)：

Js代码

1. <script type="text/javascript">   
2.             function S(){   
3.                 this.s = "s";   
4.                 this.s1 = "s1";   
5.              }   
6.             function C(){   
7.                 this.c = "c";   
8.                 this.c1 = "c1";   
9.              }   
10.              Ext.extend(C,S,{s1:"by c overload"});   
11.             var c = new C();   
12.              alert(c.s); //undefind   
13.              alert(c.s1); //by c overload   
14.          </script>  

<script type="text/javascript">   function S(){    this.s = "s";    this.s1 = "s1";   }   function C(){    this.c = "c";    this.c1 = "c1";   }   Ext.extend(C,S,{s1:"by c overload"});   var c = new C();   alert(c.s); //undefind   alert(c.s1); //by c overload  </script>

也可以通过如下方式来实现类的继承

Js代码

1. <script type="text/javascript">   
2.             function S(){   
3.              }   
4.              S.prototype.s = "s";   
5.              S.prototype.s1 = "s1";   
6.              C = Ext.extend(S,{s1:"by c overload"});   
7.             var c = new C();   
8.              alert(c.s); //s   
9.              alert(c.s1); //by c overload   
10.          </script>  

<script type="text/javascript">   function S(){   }   S.prototype.s = "s";   S.prototype.s1 = "s1";   C = Ext.extend(S,{s1:"by c overload"});   var c = new C();   alert(c.s); //s   alert(c.s1); //by c overload  </script>

此时，C是子类，S是父类

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