Variables in JavaScript

Variables in JavaScript are containers for storing data values. They allow you to store, modify, and use information throughout your program, such as numbers, text, or more complex data types156.

Declaring Variables

You can declare variables in JavaScript in several ways:

• Automatically (not recommended):

  x = 5;
  
  

  This creates a global variable if not declared inside a function, but it’s considered bad practice

• Using var:

  var x = 5;
  
  

  var is function-scoped and was the traditional way to declare variables before ES6

• Using let:

  let y = 6;
  
  

  let is block-scoped and is preferred for variables that may change their value

• Using const:

  const PI = 3.14;
  
  

  const is block-scoped and used for variables whose values should not change

Assigning Values

You can assign a value to a variable either when you declare it or later in your code:

let carName;
carName = "Volvo";

Or in one line:

let carName = "Volvo";

Variables can be updated (except those declared with const)

Naming Rules

• Variable names can contain letters, digits, underscores (\_), and dollar signs ($).
• Names must begin with a letter, underscore, or dollar sign.
• Names are case-sensitive (myVar and myvar are different).
• Reserved keywords (like function or class) cannot be used as variable names

Example