JavaScript Variables

Published on 14 May 2026
Reading Time 3
Number of Words 465

Learning Javascript Javascript

In JavaScript, a variable is a named storage location that holds a value. Variables allow you to store data and manipulate it throughout your program. For example:

let age = 25; const name = "John";

Declaring Variables

JavaScript provides three main ways to declare variables:

var: This is the oldest way to declare variables. It has function scope, meaning the variable is available within the function it is declared in, even if it’s inside a block like if or for. Its use is discouraged in modern code due to unexpected behaviors.
let: Introduced in ECMAScript 6 (ES6), let declares variables with block scope, which means the variable is only available within the block where it is defined. This prevents many scope-related errors.
const: Also introduced in ES6, const is used to declare variables whose value cannot be reassigned after the initial assignment. Like let, it has block scope.

let x = 10; // a variable that can change its value const y = 20; // a constant whose value cannot change

Assigning Values

Once a variable is declared, you can assign a value using the assignment operator =:

let message; message = "Hello, world!";

You can also declare and assign a value in one line:

let greeting = "Welcome!";

Rules for Variable Names

When naming variables in JavaScript, follow these rules:

Names can contain letters, digits, underscores (_), and dollar signs ($).
Names must start with a letter, underscore, or dollar sign.
Variable names are case-sensitive (age and Age are different).
Names cannot be reserved keywords (like let, const, function, etc.).

Best Practices

Use const by default to prevent accidental changes to values that should remain constant.
Use let when you need to reassign a variable’s value.
Avoid using var due to its unpredictable function scope.
Choose descriptive variable names that clearly indicate their purpose.

Code example with variables without errors

<html>
    <head>
        <title>TODO supply a title</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
    </head>
    <body>
        <div>TODO write content</div>
        <script type="text/javascript">
            console.log(text2);
            
            const name = "myName";
            let text = 'myLetText';
            var text2 = 'myVarText';

            console.log(name);
            console.log(text);
            console.log(text2);
        </script>
    </body>
</html>