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    Set.prototype.forEach()

    This is an experimental technology, part of the Harmony (ECMAScript 6) proposal.
    Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

    Summary

    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

    Printing 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 6 (ECMA-262)
    The definition of 'Set.prototype.forEach' in that specification.
    Draft 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 iOS 8

    See also

    Document Tags and Contributors

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