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handler.enumerate()

Obsolete
This feature is obsolete.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.

The handler.enumerate() method used to be a trap for for...in statements, but has been removed from the ECMAScript standard in edition 7 and is deprecated in browsers.

Syntax

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

Parameters

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

target
The target object.

Return value

An iterator object.

Description

The handler.enumerate method is a trap for for...in statements.

Interceptions

This trap can intercept these operations:

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)
The definition of '[[Enumerate]]' in that specification.
Standard Initial definition. Removed in ECMAScript 2016 (ES7).

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support No support No support [1] No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 37.0 (37) [1] No support No support No support

[1] This feature was supported from version 37 to version 46, but has been removed to comply with the latest ECMAScript standard, see bug 1246318.

See also

Document Tags and Contributors

 Contributors to this page: eduardoboucas, fscholz, ziyunfei, arai
 Last updated by: eduardoboucas,