Web/JavaScript/Reference/Global objects/Map/forEach

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

Syntax

myMap.forEach(callback([value][, key][, map])[, thisArg])

Parameters

callback: Function to execute for each entry of myMap. It takes the following arguments:

value Optional Value of each iteration. key Optional Key of each iteration. map Optional The map being iterated (myMap in the above Syntax box).

thisArg Optional: Value to use as this when executing callback.

Return value

undefined.

Description

The forEach method executes the provided callback once for each key of the map which actually exist. It is not invoked for keys 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 entry's value
the entry's key
the Map object being traversed

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.

Each value is visited once, except in the case when it was deleted and re-added before forEach has finished. callback is not invoked for values deleted before being visited. New values added before forEach has finished will be visited.

Examples

Printing the contents of a Map object

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

function logMapElements(value, key, map) {
    console.log(`map.get('${key}') = ${value}`)
}
new Map([['foo', 3], ['bar', {}], ['baz', undefined]]).forEach(logMapElements)
// logs:
// "map.get('foo') = 3"
// "map.get('bar') = [object Object]"
// "map.get('baz') = undefined"

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Map.prototype.forEach' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`forEach`	Chrome Full support 38	Edge Full support 12	Firefox Full support 25	IE Full support 11	Opera Full support 25	Safari Full support 8	WebView Android Full support 38	Chrome Android Full support 38	Firefox Android Full support 25	Opera Android Full support 25	Safari iOS Full support 8	Samsung Internet Android Full support 3.0	nodejs Full support 0.12

Legend

Full support: Full support