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JavaScript Hello World 

JavaScript Hello World 



Click on RUN button to see the output

Javascript Online Compiler

Write, Run & Share Javascript code online using OneCompiler's JS online compiler for free. It's one of the robust, feature-rich online compilers for Javascript language. Getting started with the OneCompiler's Javascript editor is easy and fast. The editor shows sample boilerplate code when you choose language as Javascript. OneCompiler also has reference programs, where you can look for the sample programs and start learning. Happy learning!!

About Javascript

Javascript(JS) is a object-oriented programming language which adhere to ECMA Script Standards. Javascript is required to design the behaviour of the web pages.

Key Features

  • Open-source
  • Just-in-time compiled language
  • Embedded along with HTML and makes web pages alive
  • Originally names as LiveScript.
  • Executable in both browser and server which has Javascript engines like V8(chrome), SpiderMonkey(Firefox) etc.

Syntax help

variable declaration

varVar is used to declare variables(old way of declaring variables)Function or global scope
letlet is also used to declare variables(new way)Global or block Scope
constconst is used to declare const values. Once the value is assigned it can not be modifiedGlobal or block Scope


An array is a collection of items or values.


let arrayName = [value1, value2,..etc];
// or
let arrayName = new Array("value1","value2",..etc);


let mobiles = ["iPhone", "Samsung", "Pixel"];

// accessing an array

// changing an array element
mobiles[3] = "Nokia";

Arrow functions

Arrow Functions helps developers to write code in concise way, it’s introduced in ES6. Arrow functions can be written in multiple ways. Below are couple of ways to use arrow function but it can be written in many other ways as well.


() => expression


const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
const squaresOfEvenNumbers = numbers.filter(ele => ele % 2 == 0)
                                    .map(ele => ele ** 2);


1. If:

IF is used to execute a block of code based on a condition.


    // code

2. If-Else:

Else part is used to execute the block of code when the condition fails.


    // code
} else {
    // code

3. Switch:

Switch is used to replace nested If-Else statements.


    case 'value1' :
    case 'value2' :
    default :

4. For

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  

5. While

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of ierations is not known in advance.

while (condition) {  
  // code 

6. Do-While

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
  // code 
} while (condition); 


ES6 introduced classes along with OOPS concepts in JS. Class is similar to a function which you can think like kind of template which will get called when ever you initialize class.


class className {
  constructor() { ... } //Mandatory Class method
  method1() { ... }
  method2() { ... }


class Mobile {
  constructor(model) {
    this.name = model;

mbl = new Mobile("iPhone");

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Reference Programs:


No tags available for JavaScript

How to use?

Choose the language in which you want to run your program, by clicking the button next to Run. And then write your code in the code box, You can use the auto complete snippets and warnings and errors which helps you to write better code faster way.
Once you are done writing your code click the Run button, now the code will be submitted to OneCompiler and you will see the results in a second.

How to contribute?

Please fork OneCompiler repository and contribute us by adding more languages or the features to the existing OneCompiler backend.
You can also contibute to the community by adding more programs which users can search and use as base code for their programs.

API & More

You can embed OneCompiler into your own website. That helps your website users to write and test their programs within your website.
If you want to run and see the results from your backend you can utilize the OneCompiler API by integrating it with your backend.