JS Array Prototype ForEach

JavaScript Array prototype forEach

The forEach() method executes a provided function once per array element.

Syntax

arr.forEach(callback[, thisArg])

Parameters

• callback Function to execute for each element, taking three arguments:

  • currentValue The current element being processed in the array.
  • index The index of the current element being processed in the array.
  • array The array that forEach is being applied to.

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

MDN link | MSDN link

Description

forEach() executes the provided callback once for each element present in the array in ascending order. It is not invoked for index properties that have been deleted or are uninitialised (i.e. on sparse arrays). Unlike map() or reduce() it always returns the value undefined and is not chainable. The typical use case is to execute side effects at the end of a chain.

Examples

function logArrayElements(element, index, array) {
  console.log('a[' + index + '] = ' + element);
}

// Note elision, there is no member at 2 so it isn't visited
[2, 5, , 9].forEach(logArrayElements);
// logs:
// a[0] = 2
// a[1] = 5
// a[3] = 9

// Create an array.
var numbers = [10, 11, 12];

// Call the addNumber callback function for each array element.
var sum = 0;
numbers.forEach(
    function addNumber(value) { sum += value; }
);

document.write(sum);
// Output: 33