JavaScript Array Iteration Methods

JavaScript Array Iteration Methods


Array iteration methods operate on every array item.


Array.forEach()

The forEach() method calls a function (a callback function) once for each array element.

Example

var txt = "";
var numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);

function myFunction(value, index, array) {
  txt = txt + value + "<br>";
}
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Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

The example above uses only the value parameter. The example can be rewritten to:

Example

var txt = "";
var numbers = [45, 4, 9, 16, 25];
numbers.forEach(myFunction);

function myFunction(value) {
  txt = txt + value + "<br>";
}
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Array.forEach() is supported in all browsers except Internet Explorer 8 or earlier:

Yes 9.0 Yes Yes Yes

Array.map()

The map() method creates a new array by performing a function on each array element.

The map() method does not execute the function for array elements without values.

The map() method does not change the original array.

This example multiplies each array value by 2:

Example

var numbers1 = [45, 4, 9, 16, 25];
var numbers2 = numbers1.map(myFunction);

function myFunction(value, index, array) {
  return value * 2;
}
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Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

When a callback function uses only the value parameter, the index and array parameters can be omitted:

Example

var numbers1 = [45, 4, 9, 16, 25];
var numbers2 = numbers1.map(myFunction);

function myFunction(value) {
  return value * 2;
}
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Array.map() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes


Array.filter()

The filter() method creates a new array with array elements that passes a test.

This example creates a new array from elements with a value larger than 18:

Example

var numbers = [45, 4, 9, 16, 25];
var over18 = numbers.filter(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}
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Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

In the example above, the callback function does not use the index and array parameters, so they can be omitted:

Example

var numbers = [45, 4, 9, 16, 25];
var over18 = numbers.filter(myFunction);

function myFunction(value) {
  return value > 18;
}
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Array.filter() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Array.reduce()

The reduce() method runs a function on each array element to produce (reduce it to) a single value.

The reduce() method works from left-to-right in the array. See also reduceRight().

The reduce() method does not reduce the original array.

This example finds the sum of all numbers in an array:

Example

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction);

function myFunction(total, value, index, array) {
  return total + value;
}
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Note that the function takes 4 arguments:

  • The total (the initial value / previously returned value)
  • The item value
  • The item index
  • The array itself

The example above does not use the index and array parameters. It can be rewritten to:

Example

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction);

function myFunction(total, value) {
  return total + value;
}
Try it Yourself »

The reduce() method can accept an initial value:

Example

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduce(myFunction, 100);

function myFunction(total, value) {
  return total + value;
}
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Array.reduce() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Array.reduceRight()

The reduceRight() method runs a function on each array element to produce (reduce it to) a single value.

The reduceRight() works from right-to-left in the array. See also reduce().

The reduceRight() method does not reduce the original array.

This example finds the sum of all numbers in an array:

Example

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduceRight(myFunction);

function myFunction(total, value, index, array) {
  return total + value;
}
Try it Yourself »

Note that the function takes 4 arguments:

  • The total (the initial value / previously returned value)
  • The item value
  • The item index
  • The array itself

The example above does not use the index and array parameters. It can be rewritten to:

Example

var numbers1 = [45, 4, 9, 16, 25];
var sum = numbers1.reduceRight(myFunction);

function myFunction(total, value) {
  return total + value;
}
Try it Yourself »

Array.reduce() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Array.every()

The every() method check if all array values pass a test.

This example check if all array values are larger than 18:

Example

var numbers = [45, 4, 9, 16, 25];
var allOver18 = numbers.every(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}
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Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

When a callback function uses the first parameter only (value), the other parameters can be omitted:

Example

var numbers = [45, 4, 9, 16, 25];
var allOver18 = numbers.every(myFunction);

function myFunction(value) {
  return value > 18;
}
Try it Yourself »

Array.every() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Array.some()

The some() method check if some array values pass a test.

This example check if some array values are larger than 18:

Example

var numbers = [45, 4, 9, 16, 25];
var someOver18 = numbers.some(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}
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Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

Array.some() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Array.indexOf()

The indexOf() method searches an array for an element value and returns its position.

Note: The first item has position 0, the second item has position 1, and so on.

Example

Search an array for the item "Apple":

var fruits = ["Apple", "Orange", "Apple", "Mango"];
var a = fruits.indexOf("Apple");
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Array.indexOf() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Syntax

array.indexOf( item, start)
item Required. The item to search for.
start Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the end.

Array.indexOf() returns -1 if the item is not found.

If the item is present more than once, it returns the position of the first occurrence.


Array.lastIndexOf()

Array.lastIndexOf() is the same as Array.indexOf(), but searches from the end of the array.

Example

Search an array for the item "Apple":

var fruits = ["Apple", "Orange", "Apple", "Mango"];
var a = fruits.lastIndexOf("Apple");
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Array.lastIndexOf() is supported in all browsers except Internet Explorer 8 or earlier.

Yes 9.0 Yes Yes Yes

Syntax

array.lastIndexOf( item, start)
item Required. The item to search for
start Optional. Where to start the search. Negative values will start at the given position counting from the end, and search to the beginning

Array.find()

The find() method returns the value of the first array element that passes a test function.

This example finds (returns the value of) the first element that is larger than 18:

Example

var numbers = [4, 9, 16, 25, 29];
var first = numbers.find(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}
Try it Yourself »

Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

Array.find() is not supported in older browsers. The first browser versions with full support is listed below.

45 12 25 8 32

Array.findIndex()

The findIndex() method returns the index of the first array element that passes a test function.

This example finds the index of the first element that is larger than 18:

Example

var numbers = [4, 9, 16, 25, 29];
var first = numbers.findIndex(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}
Try it Yourself »

Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

Array.findIndex() is not supported in older browsers. The first browser versions with full support is listed below.

45 12 25 8 32