My First Steps in JavaScript: A Simple Breakdown

Source: Dev.to

Variables in JavaScript

let

Used for values that can change later.

let age = 20;
age = 21;

const

Used when the value should not be changed.

const PI = 3.14;

var

The old way of declaring variables. Not recommended now because it creates confusion with scope.

Data Types in JavaScript

Primitive Types

• String → "Hello"
• Number → 23, 45.6
• Boolean → true or false
• Null → empty value
• Undefined → no value assigned
• BigInt → very large numbers
• Symbol → unique values

Non-Primitive Types

• Object
• Array
• Function

Undefined vs Null

undefined

Means a variable exists but has no value yet.

let x;
console.log(x); // undefined

null

Means intentionally empty. We set it manually when something should have no value.

let data = null;