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This feature is obsolete.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 ES2016 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.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic support
DeprecatedNon-standard
Chrome No support NoEdge No support NoFirefox No support 37 — 47IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile No support NoFirefox Android No support 37 — 47Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support Nonodejs No support No

Legend

No support  
No support
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.

See also

Document Tags and Contributors

Contributors to this page: mfuji09, fscholz, nmve, kdex, eduardoboucas, ziyunfei, arai
Last updated by: mfuji09,