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:

• Property enumeration / 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

Not part of any standard.

Browser compatibility

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

See also

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