JS Proxy enumerate()

本文目录结构

已废弃
This feature is obsolete.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.

代理方法handler.enumerate()决定了被代理对象在for...in中的行为。不过这个方法已经在ES2016标准中被移除了。

语法

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

参数

下列参数将会被用以调用 enumerate 方法。this将会指向处理器对象。

target

被代理的目标对象。

Return value

该方法应当返回一个迭代器

描述

handler.enumerate 方法决定了被代理对象在for...in时的行为。

触发条件

这些操作可以触发这个方法。

• for…in: for (var name in proxy) {...}
• Reflect.enumerate()

Invariants

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

• The enumerate method must return an object.

Examples

The following code traps for...in statements.

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].

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262)[[Enumerate]]	Standard	Initial definition. Removed in ECMAScript 2016.

See also

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