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handler.isExtensible()

JavaScript handler.isExtensible()方法

handler.isExtensible()方法是Object.isExtensible()的陷阱。我们通常可以用于记录或审核对Object.isExtensible的调用(确定对象是否"可扩展")。

语法

isExtensible: function(target)

参数

target:目标对象。

返回值

返回布尔值。

浏览器支持

Chrome 兼容性未知
Edge 兼容性未知
Firefox 31
Opera 兼容性未知

示例1

var x = { foo: 1 };
var proxy = new Proxy(x, {
  isExtensible: function(target) {
    document.writeln('in isExtensible');
    //expected output: in isExtensible
 return Object.isExtensible(target);
  }
});
document.writeln(Object.isExtensible(proxy));
//expected output: true
document.writeln("<br/>")
Object.preventExtensions(proxy);
document.writeln(Object.isExtensible(proxy));
//expected output: false
输出:
in isExtensible true
in isExtensible false中

示例2

const pro={
too:1 }
const proxy = new Proxy(pro, {
  isExtensible: function(target) {
    document.writeln(' in value : ');
    return true;
  }
});
document.writeln(Object.isExtensible(proxy));
//expected output: in value : true
输出:
in value:false

示例3

var a = {
  canEvolve: true
};
var b = {
  isExtensible(target) {
    return true;
  },
   };
const proxy1 = new Proxy(a, b);
document.writeln(Object.isExtensible(proxy1));
// expected output: true
输出:
true
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