Array.prototype[@@unscopables]

The @@unscopable symbol property contains property names that were not included in the ECMAScript standard prior to the ES2015 version. These properties are excluded from with statement bindings.

Description

The default array properties that are excluded from with bindings are:

See Symbol.unscopables for how to set unscopables for your own objects.

Property attributes of Array.prototype[@@unscopables]
Writable no
Enumerable no
Configurable yes

Examples

Use in with environments

The following code works fine in ES5 and below. However, in ECMAScript 2015 and later, the Array.prototype.keys() method was introduced. That means that inside with environments, "keys" would now be the method and not the variable. This is where now the built-in @@unscopables Array.prototype[@@unscopables] symbol property comes into play and prevents that some of the Array methods are being scoped into the with statement.

var keys = [];

with (Array.prototype) {
  keys.push('something');
}

Object.keys(Array.prototype[Symbol.unscopables]);
// ["at", "copyWithin", "entries", "fill", "find", "findIndex",
//  "includes", "keys", "values"]

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'Array.prototype[@@unscopables]' in that specification.

Browser compatibility

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See also