JavaScript Array Iteration Methods






<!--
main_leaderboard, all: [728,90][970,90][320,50][468,60]
-->



JavaScript Array Iteration Methods



❮ Previous
Next ❯


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






<!--
mid_content, all: [300,250][336,280][728,90][970,250][970,90][320,50][468,60]
-->




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



❮ Previous
Next ❯

-

Popular posts from this blog

Greedy Best First Search implementation in Rust

Image
Clash Royale CLAN TAG #URR8PPP .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty margin-bottom:0; up vote 1 down vote favorite I have implemented a Greedy Best First Search algorithm in Rust, since I couldn't find an already implemented one in the existing crates. I have a small pet project I do in Rust, and the Greedy BFS is at the core of it. The algorithm is designed to be as flexible as possible. Theoretically, this algorithm could be used as a greedy depth-first search or as a greedy a*. I want to design a good algorithm that I could later use in any other project needing it, not only this one. I am quite new to Rust and this is the second project I do in this language. Also, I am new to writing optimized algorithms. Since this search will be called often, my main concern is performance. What are some tips and tricks to make the algorithm perform better? Of course any other critique and comment is welcome. Bellow is the code: //! Here is
Read more

Function to Return a JSON Like Objects Using VBA Collections and Arrays

Image
Clash Royale CLAN TAG #URR8PPP .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty margin-bottom:0; up vote 1 down vote favorite My goal is to create a compact function that can create a JSON Like object from JSON string. I want a function with a small footprint that I or anyone who wants to use it, can simply paste into a module and use. At 61 lines of code, I am happy with its size and portability. Here is an image of JSON Object created from string data using a ScriptControl . Although the Locals Window displays the properties and values correctly, the object itself is extremely difficult to work with. This image shows an object created using getJSONCollection . Because it is made of VBA Collections and Arrays, it is very easy to work with. Option Explicit Private Function getJSONCollection(ByVal Value As Variant, Optional ScriptEngine As Object) As Variant Const DELIMITER As String = "||" Dim col As Collection, JSON As Object, KeyNam
Read more

C++11 CLH Lock Implementation

Image
Clash Royale CLAN TAG #URR8PPP .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty margin-bottom:0; up vote 1 down vote favorite 1 As a hobbyist programmer I have been reading "The Art of Multiprocessor Programming" (Herlihy, Maurice; Shavit, Nir) and converting the Java spin locks into C++ - I have enjoyed this and learned a lot. I have implemented the CLH spin queue lock (due to Travis Craig, Erik Hagersten, and Anders Landin) but I feel unhappy about the way that I have the raw pointers interacting with smart pointers and would be grateful for code review advice. As I understand it I must use a smart pointer, in this case std::unique_ptr , for my thread local node pointer or the lock will not deallocate properly and the clh_lock will leak. But... I also have no choice but to use a raw atomic tail queue pointer in order access the atomic exchange member function. Therefore, I have to come up with some combination of either, raw or smart
Read more