Data Types in Javascript

Hi, everyone. I decided to start writing about my knowledge in JS to help those who are beginners in dev community.

I hope this article would be helpful to you :)

---

First of all... What is a variable?

A Variable is a container which stores values.
This value can be changed when we use the word 'let' to declare a variable.

We have the option to declare a variable using the word 'const', too, but this value will not be changing, so be careful.

---

In Javascript, we have 7 types of data:

let name = 'Debs'; // String (a sequence of text)
let age = 24; // Number
let isGraduated = true; // Boolean (this is a true or false value)
let team; // Undefined (there's no value defined)
let food = null; // Null (represents the intentional absence of any object value)
let symbol = Symbol(); // Symbol
let newObject = {}; // Object

These are primitive data, it means that it is not mutable (except for the objects).

---

If you are not sure about the type of the variable you are working with, there is a way to discover it by using the command 'typeof' inside the console.log

Example:

let name = 'Debs';
console.log(typeof name); // returns string

Comments

[Jon Randy 🎖️]

You missed bigint.

console.log(typeof 10n)  // bigint

JS has 7 primitive data types: string, number, boolean, null, undefined, symbol and bigint. Everything else is an object (which isn't a primitive).

Sometimes though, depending on how you define a value - the result of typeof may surprise you:

let myNum = 3
console.log(typeof myNum)  // number
console.log(myNum * 7)  // 21

let myOtherNum = new Number(3)
console.log(typeof myOtherNum )  // object
console.log(myOtherNum * 7)  // 21

Also, be careful how you use the word 'changing' when talking about const - it is better to say a const cannot be redefined. You are perfectly free to change the properties of an object declared as a constant:

const num = 3
num = 4  // TypeError

const obj = {}
obj.num = 6  // No problem