This feature is obsolete.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.


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


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

The target object.

Return value

An iterator object.


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


This trap can intercept these operations:


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

  • The enumerate method must return an object.


The following code traps for...in statements.

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


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

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support No No37 — 47 No No No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support No No No37 — 47 No No No

See also

Document Tags and Contributors

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