Variables

In JavaScript, variables are used to store data values that can be used and manipulated throughout the code. Variables in JavaScript can hold different types of data, such as numbers, strings, boolean values, arrays, objects, and functions.

There are three keywords used to declare variables - var, let, and const.

The syntax to create a variable is first the keyword, a space, the name we are giving the variable, an equal sign, the value we are assigning the variable, and then a semicolon.

var firstName = 'Salvador';
let lastName = 'Dali';
const favouritePet = 'Babou';

Variables declared with var have function scope, which means they are accessible throughout the function in which they are declared. Variables declared with let and const have block scope, which means they are only accessible within the block in which they are declared.

In JavaScript, variables can also be re-assigned new values using the assignment operator =.

It's important to note that const variables cannot be re-assigned, and attempting to do so will result in a syntax error. Additionally, all variables in JavaScript are hoisted to the top of their scope, which means that they are declared before any code is executed. This can sometimes lead to unexpected behavior, so it's important to understand how hoisting works in JavaScript.

var

var is the ES5 way of declaring a variable. This is a generic variable keyword. Variables created with var can be changed without causing errors.

const

const is a variable that cannot be changed later in the code.

let

let is a new ES6 variable keyword. This will assign a variable much like var, but with a little bit different behavior. Most notably, it differs by creating "block level scope".

Summary

• var can be re-assigned and changed
• let can be re-assigned but not changed
• const cannot be re-assigned nor changed