JavaScript Data Types Deep Dive: Learn Primitives and References Data Types in JS | Data Types in Js

Learn JavaScript Data Types | JavaScript Data Types Deep Dive: Learn Primitives and References Data Types in JS

When we create variables in JavaScript, each one has a type. These types fall into two main groups: primitive types and reference types. The main difference between them is how they are stored and accessed in memory.

• Primitive Types - Stored directly in the location that the variable is accessed.
• Reference Types (Objects) - Accessed by reference.

Primitive Data Types In JavaScript

There are 7 primitive data types in JavaScript:

• String - A sequence of characters, written with single or double quotes.
• Number - Represents both whole numbers and decimals.
• Boolean - Represents true or false values.
• Null - Represents an intentional absence of any object value.
• Undefined - A variable without a value is considered undefined.
• Symbol - A unique identifier.
• BigInt - Used for numbers larger than what the regular Number type can handle.

Example Code

const city = 'Tokyo'; // String
const height = 180; // Number
const isStudent = false; // Boolean
const officeRoom = null; // Null
let age; // Undefined
const uniqueKey = Symbol('uniqueKey'); // Symbol
const largeValue = 987654321123456789n; // BigInt
  

Dynamic vs Static Types

JavaScript is a dynamically-typed language. This means that we don’t have to set the type of variable—it’s set automatically based on the value. For example, a variable might be a string, but you can change it to a number later.

Some other languages, like Java, are statically-typed, where you must set the type of a variable when creating it. TypeScript, an extension of JavaScript, also allows you to set types like this:

const salary: number = 50000;

This makes code more secure but also requires more effort.

Using the typeof Operator In JavaScript

To check a variable’s type, you can use the typeof operator:

console.log(typeof city); // Output: 'string'

Note: typeof returns object for null due to an early design error in JavaScript.

Reference Data Types (Objects)

In JavaScript, reference types include arrays, objects, and functions. These types are stored by reference, meaning the variable holds a reference to the location in memory, not the actual value.

Arrays In JavaScript

Arrays are lists of values, for example:

const grades = [90, 85, 92];

Objects In JavaScript

Objects contain data with key-value pairs:

const vehicle = {
  type: 'car',
  color: 'blue'
};

Functions In JavaScript

Functions are blocks of code that perform a specific task:

const greet = function() {
  return 'Hello, World!';
};

greet(); // Outputs: 'Hello, World!'

Note: In JavaScript, functions are also considered objects, but they have the special ability to be called or invoked.

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The Ultimate Guide to Variables in JavaScript: Syntax, Naming, and Reassignment | A Beginner’s Guide to let, const, and var

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