The forEach() method of Set instances executes a provided function once
for each value in this set, in insertion order.
Syntax
forEach(callbackFn)
forEach(callbackFn, thisArg)
Parameters
callback- : A function to execute for each entry in the set. The function is called with the following arguments:
value- : Value of each iteration.
key- : Key of each iteration. This is always the same as
value.
- : Key of each iteration. This is always the same as
set- : The set being iterated.
- : A function to execute for each entry in the set. The function is called with the following arguments:
thisArg- : A value to use as
thiswhen executingcallbackFn.
- : A value to use as
Return value
None (undefined).
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
Setobject 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"