Introduction

JavaScript is a powerful script programming language that commonly used for web development (it can also be used for other purposes too, but web development is the most popular use). With endless support libraries and frameworks, JavaScript is growing strongly.

Execute JS Code

• Nodejs: The most popular environment for executing JS code, with the use of V8 engines. You can install Nodejs here: Download | Node.js (nodejs.org). After installing successfully Node to your computer, you can run your .js files by doing this in your Command-line/Powershell
• Online IDE: There are many online IDEs that support editing and compiling JS code. Note that you can choose either Nodejs or VanillaJS for development (which technically are both JavaScript).
• Browser Devtool: Your browsers (Google, Microsoft Edge, Firefox,...) also support V8 engines to execute your code! You can go to More (3-dot icon at the top right bar) > More Tools > Developer Tool, or using Ctrl+Shift+I/F12

Data Types

• String
• Number
• Array
• Object
• Boolean
• Null
• Undefined

Variables

To declare your variables, you must use keywords (var, let, or const). For example:

const num = 1; // declare variable num with initial value of 1.
console.log(num); // Print 1 to the console
const maybeNum; // declare variable maybeNum without initial value. You must assign a value afterward before running the code.

Here are some key differences between these 3 keywords: