In this JavaScript tutorial, we are going to learn about JavaScript variables.
What are Variables?
- JavaScript variables act as a container that are used to store data.
- In JavaScript let, var, and const are used to declare variables.
JavaScript Variable Naming Rules
JavaScript follows some rules to declare variables and these rules are:
- JavaScript variable names can contain letters, digits, underscores, and dollar signs.
- Variable names cannot start with a digit.
- In JavaScript variable names are case-sensitive, which means that "GeeksHelp" and "geekshelp" are two different variables.
- JavaScript variables must start with a letter, underscore, or dollar sign.
- You cannot use reserved keywords as variable names, such as "var", "function", or "switch".
- Variable names should not contain spaces or special characters (except for underscores and dollar signs).
JavaScript Variables
1). let
- It is used to declare a block-scoped variable.
- The 'let' keyword is introduced in ES6(ECMAScript2015). and it is an alternative to the 'var' keyword.
- The value of let variable can be changed.
- In different block, value can be different.
let x;
In this example the let is used to declare the variable and x is the variable name.
2). var
- var keyword in JavaScript is also used to declare a variable.
- Variables declared with var have function scope or global scope, depending on where they are declared.
- Two variables name using var keyword cannot be the same.
var x;
In this example the var is used to declare the variable and x is the variable name.
3). const
- const is used to declare a variable whose value will not be changed.
- Variable using const must be initialized during the declaration.
- The const keyword was also introduced in ES6. And const variables are block-scoped.
const x = 'Geeks Help';
In this example the const is used to declare the variable and x is the variable name and 'Geeks Help' is the value assigned to the x variable.
Difference Between let, var, and const in JavaScript
let |
var |
const |
| The scope of a let variable is block scope. | Declare global scope variables. | Declared with constant values. |
| Value can be changed. | Value will be same in every block. | It has global level scope. |
| Different block different value. | Two variables name cannot be same. | Declared using const keyword. |
