Set.prototype.forEach()
The forEach()
method executes a provided function once
for each value in the Set
object, in insertion order.
Syntax
// Arrow function
forEach(() => { /* ... */ } )
forEach((value) => { /* ... */ } )
forEach((value, key) => { /* ... */ } )
forEach((value, key, set) => { /* ... */ } )
// Callback function
forEach(callbackFn)
forEach(callbackFn, thisArg)
// Inline callback function
forEach(function() { /* ... */ })
forEach(function(value) { /* ... */ })
forEach(function(value, key) { /* ... */ })
forEach(function(value, key, set) { /* ... */ })
forEach(function(value, key, set) { /* ... */ }, thisArg)
Parameters
callback
-
Function to execute for each element, taking three arguments:
value
,key
-
The current element being processed in the
Set
. As there are no keys inSet
, the value is passed for both arguments. set
-
The
Set
object whichforEach()
was called upon.
thisArg
-
Value to use as
this
when executingcallbackFn
.
Return value
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 key
- the
Set
object being traversed
There are no keys in Set
objects, however, so the first two arguments are
both values contained in the Set
. This is to make it
consistent with other 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.
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 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 a 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 |
---|
ECMAScript Language Specification # sec-set.prototype.foreach |
Browser compatibility
BCD tables only load in the browser