The forEach()
method executes a provided function once per each key/value pair in the Map
object, in insertion order.
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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 executingcallback
.
Return value
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.
forEach
executes the callback
function once for each element in the Map
object. It does not return a value.
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
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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