JavaScript Array Iteration Methods






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JavaScript Array Iteration Methods



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Array iteration methods operate on every array item.



Array.forEach()


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



Example



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

function myFunction(value, index, array) {
   
txt = txt + item + "<br>";
}

Try it Yourself »


Note that the function takes 3 arguments:



  • The item value

  • The item index

  • The array itself


Array.forEach() is not supported in Internet Explorer 8 or earlier:




















Method
forEach() Yes 9.0 Yes Yes Yes




Array.map()


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


This example multiplies each array value by 2:



Example



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

function myFunction(value, index, array) {
    return val * 2;
}

Try it Yourself »

Note that the function takes 3 arguments:



  • The item value

  • The item index

  • The array itself


The map() method calls the provided function once for each element in an
array.


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


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


Array.map() is not supported in Internet Explorer 8 or earlier.




















Method
map() Yes 9.0 Yes Yes Yes






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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 equal to or larger than 18:



Example



var numbers = [4, 9, 16, 25];
var over18 =
numbers.filter(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.filter() is not supported in Internet Explorer 8 or earlier.




















Method
filter() Yes 9.0 Yes Yes Yes



Array.reduce()


The reduce() method reduces an array to a single variable.



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



Example



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


Array.reduce() is not supported in Internet Explorer 8 or earlier.




















Method
reduce() Yes 9.0 Yes Yes Yes




Array.every()


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



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



Example



var numbers = [4, 9, 16, 25, 29];
var allOver18 =
numbers.every(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.reduce() is not supported in Internet Explorer 8 or earlier.




















Method
every() Yes 9.0 Yes Yes Yes




Array.indexOf()


Search 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 = ["Banana", "Orange", "Apple", "Mango"];
var a = fruits.indexOf("Apple");

Try it Yourself »


Array.indexOf() is not supported in Internet Explorer 8 or earlier.




















Method
indexOf() 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 occurence.



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 = ["Banana", "Orange", "Apple", "Mango"];
var a = fruits.lastIndexOf("Apple");

Try it Yourself »


Array.lastIndexOf() is not supported in Internet Explorer 8 or earlier.




















Method
lastIndexOf() 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



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