JavaScript Basics: Variables and Data Types

Are you ready to dive into the exciting world of JavaScript? If you're new to programming, don't worry! JavaScript is a great language to start with, and we're here to guide you through the basics.

In this article, we'll be focusing on variables and data types in JavaScript. These are the building blocks of any program, so it's important to understand them thoroughly. Let's get started!

What are Variables?

Variables are containers that hold values. These values can be anything from numbers to strings to objects. Variables are used to store and manipulate data in a program.

In JavaScript, variables are declared using the var, let, or const keywords. The var keyword was used in older versions of JavaScript, but it's still valid. The let and const keywords were introduced in ES6 (ECMAScript 2015) and are now the preferred way of declaring variables.

// Declaring a variable using var
var myVariable = 10;

// Declaring a variable using let
let myOtherVariable = "Hello, world!";

// Declaring a variable using const
const myConstantVariable = true;

Notice that when declaring a variable using const, you must assign a value to it immediately. Once a value is assigned to a const variable, it cannot be changed.

Data Types

Now that we know how to declare variables, let's talk about data types. In JavaScript, there are six primitive data types:


The Number data type represents numeric values. This can be anything from integers to floating-point numbers.

let myNumber = 42;
let myFloat = 3.14;


The String data type represents text. Strings are enclosed in either single or double quotes.

let myString = "Hello, world!";
let myOtherString = 'This is a string too.';


The Boolean data type represents true or false values.

let myBoolean = true;
let myOtherBoolean = false;


The Null data type represents a null or empty value.

let myNull = null;


The Undefined data type represents a variable that has not been assigned a value.

let myUndefined;


The Symbol data type represents a unique identifier.

let mySymbol = Symbol();

Type Coercion

JavaScript is a dynamically typed language, which means that variables can change their data type at runtime. This can lead to unexpected behavior if you're not careful.

let myNumber = 42;
let myString = "42";

console.log(myNumber + myString); // "4242"

In the example above, myNumber is a number and myString is a string. When we try to add them together, JavaScript coerces myNumber into a string and concatenates the two values.

To avoid unexpected behavior, it's important to be aware of type coercion and to use strict equality (===) when comparing values.

let myNumber = 42;
let myString = "42";

console.log(myNumber === myString); // false


Variables and data types are the foundation of any program, and JavaScript is no exception. By understanding how to declare variables and the different data types available in JavaScript, you'll be well on your way to writing your own programs.

In the next article, we'll be covering operators and control structures in JavaScript. Stay tuned!

Editor Recommended Sites

AI and Tech News
Best Online AI Courses
Classic Writing Analysis
Tears of the Kingdom Roleplay
Training Course: The best courses on programming languages, tutorials and best practice
Flutter News: Flutter news today, the latest packages, widgets and tutorials
Learn GPT: Learn large language models and local fine tuning for enterprise applications
Knowledge Graph Consulting: Consulting in DFW for Knowledge graphs, taxonomy and reasoning systems
Developer Key Takeaways: Key takeaways from the best books, lectures, youtube videos and deep dives