Set.prototype.forEach()

by 3 contributors:

This is a new technology, part of the ECMAScript 2015 (ES6) standard .
This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.

The forEach() method executes a provided function once per each value in the Set object, in insertion order.

Syntax

mySet.forEach(callback[, thisArg])

Parameters

callback
Function to execute for each element.
thisArg
Value to use as this when executing callback.

Description

The forEach method executes the provided callback once for each value which actually exists in the Set object. It is not invoked for values which have been deleted. However, it is executed for values which are present but have the value undefined.

callback is invoked with three arguments:

  • the element value
  • the element value
  • the Set object being traversed

The are no keys in Set objects. However, the first two arguments are both values contained in the Set, so that the callback function is consistent with the forEach methods for Map and Array.

If a thisArg parameter is provided to forEach, it will be passed to callback when invoked, for use as its this value.  Otherwise, the value undefined will be passed for use as its this value.  The this value ultimately observable by callback is determined according to the usual rules for determining the this seen by a function.

The range of elements processed by forEach is set before the first invocation of callback. Elements which are added to the Set object after the call to forEach begins, will not be visited by callback. If existing elements of the Set object are changed, or deleted, their value as passed to callback will be the value at the time forEach visits them; elements that are deleted are not visited.

forEach executes the callback function once for each element in the Set object; it does not return a value.

Examples

Logging the contents of a Set object

The following code logs a line for each element in an Set object:

function logSetElements(value1, value2, set) {
    console.log("s[" + value1 + "] = " + value2);
}

new Set(["foo", "bar", undefined]).forEach(logSetElements);

// logs:
// "s[foo] = foo"
// "s[bar] = bar"
// "s[undefined] = undefined"

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Set.prototype.forEach' in that specification.
Standard Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 38 25.0 (25.0) 11 25 7.1
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support Not supported 38 25.0 (25.0) Not supported Not supported 8

See also

Document Tags and Contributors

Contributors to this page: fscholz, realityking, P0lip
Last updated by: fscholz,