在此页

• 句法
• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

过时
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

handler.enumerate() method used to be a trap for for...in statements, but has been removed from the ECMAScript standard in ES2016 and is deprecated in browsers.

句法

var p = new Proxy(target, {
  enumerate(target) {
  }
});
					

参数

The following parameter is passed to the enumerate 方法。 this is bound to the handler.

target

The target object.

返回值

An iterator 对象。

描述

handler.enumerate method is a trap for for...in 语句。

Interceptions

This trap can intercept these operations:

• Property enumeration / for...in: for (var name in proxy) {...}
• Reflect.enumerate()

Invariants

If the following invariants are violated, the proxy will throw a TypeError :

• enumerate method must return an object.

范例

The following code traps for...in 语句。

var p = new Proxy({}, {
  enumerate(target) {
    console.log('called');
    return ['a', 'b', 'c'][Symbol.iterator]();
  }
});
for (var x in p) { // "called"
  console.log(x);  // "a"
}                  // "b"
                   // "c"
					

The following code violates the invariant.

var p = new Proxy({}, {
  enumerate(target) {
    return 1;
  }
});
for (var x in p) {} // TypeError is thrown
					

Note: Both examples make use of the shorthand syntax for method definitions .

规范

Not part of any standard.

浏览器兼容性

Not supported anywhere. Historically supported in Firefox 37 till 46.

另请参阅

• Proxy
• handler
• for...in statements
• Reflect.enumerate()

元数据

• 最后修改： Apr 28, 2020

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