Data types in JS

JavaScriptJunior~1 min read

JavaScript has 8 basic data types. They are split into primitive and reference (object) types.

1. Primitive types (7 total)

A primitive is a value that is not an object and has no methods. They are stored by value, not by reference.

Numbers - both integers and floating-point.

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let a = 42;
let b = 3.14;

Notes:

Used for very large integers that exceed the limits of Number.

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let big = 123456789012345678901234567890n;

Adds the n suffix. Lets you work precisely with integers of any length.

Text strings in quotes: 'single', "double", or template quotes.

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let name = "Tim";
let message = `Hello, ${name}!`;

Strings are immutable - a new string is created on any change.

Logical values - true or false.

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let isAdmin = true;
let isLoggedIn = false;

Used in conditions, checks, and logical expressions.

A special value denoting "nothing" or "empty".

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let user = null;

Its type is object (a historical mistake in JavaScript that stuck).

A variable declared but with no assigned value.

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

Assigned automatically when no value is set.

A unique, immutable value often used as an object key.

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let id = Symbol('id');
let obj = { [id]: 123 };

Every Symbol is unique, even with the same description.

Stores collections of data and functions. Passed by reference, not by value.

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let user = { name: "Tim", age: 25 };
let arr = [1, 2, 3];
let func = function() {};

Object subtypes:

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