ExtJs关于Ext.extend()的说明_综合

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

<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>

<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); //salert(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

<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>

<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); //undefindalert(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

<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>

<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); //salert(c.s1); //by c overload</script>

此时，C是子类，S是父类