What Are the Data Types Supported by JavaScript?

JavaScript variables can hold different types of data values. Understanding these is fundamental for every developer. JavaScript has two main categories of data types:

1. Primitive Data Types (Immutable)

• String: Text data

  let name = "John";
  

• Number: Both integers and decimals

  let age = 25;
  let price = 99.99;
  

• Boolean: true/false

  let isActive = true;
  

• Undefined: Uninitialized variable

  let x; // undefined
  

• Null: Intentional absence of value

  let user = null;
  

• Symbol (ES6): Unique identifiers

  let id = Symbol('unique');
  

• BigInt (ES2020): Large integers

  let bigNum = 9007199254740991n;
  

2. Non-Primitive Data Types (Mutable)

• Object: Key-value pairs

  let person = { name: "John", age: 30 };
  

• Array: Ordered lists

  let colors = ["red", "green", "blue"];
  

• Function: Callable objects

  function greet() { 
    console.log("Hello!"); 
  }
  

Type Checking

Use typeof operator:

typeof "Hello" // "string"
typeof 42 // "number"
typeof true // "boolean"

Special Cases

typeof null // "object" (historical bug)
typeof [] // "object"
typeof function() {} // "function"

Pro Tip: For precise type checking, use:

Array.isArray([]) // true
Object.prototype.toString.call(null) // "[object Null]"