Lesson 8

Data Types

Data types specify the kind of value a variable can hold in JavaScript. They help the engine understand how to store and work with the data.

Primitive Data Types
Reference (Non-Primitive) Types
typeof Operator
Type Conversion

Primitive types store a single value.

String

"abc"

Sequence of characters.

let name = "Vivek";

Number

123

Integers and floating point numbers.

let age = 29;

Boolean

true

Logical values: true or false.

let isActive = true;

Undefined

undefined

Variable declared but not assigned a value.

let x;

Null

null

Intentional absence of any value.

let user = null;

Symbol

Unique and immutable value (ES6).

let id = Symbol('id');

These types can store collections of values.

Object

{ }

Collection of key-value pairs.

let person = { name: 'Vivek' };

Array

[ ]

Ordered list of values.

let numbers = [1, 2, 3];

Function

f()

Reusable block of code.

function greet() { }

Used to check the type of a value.

1typeof "Vivek";      // "string"2typeof 29;           // "number"3typeof true;         // "boolean"4typeof undefined;    // "undefined"5typeof null;         // "object" (JS quirk)6typeof {};           // "object"7typeof [];           // "object"8typeof function(){}; // "function"

Implicit (automatic)

"5" + 2;    // "52"  number becomes string"5" - 2;    // 3     string becomes numbertrue + 1;   // 2     true becomes 1

Explicit (you convert)

Number("5");    // 5String(29);     // "29"Boolean(0);     // false

Run the code to explore data types.

JavaScript

1let name = "Vivek";
2let age = 29;
3let isActive = true;
4let person = { city: "Hosur" };
5let numbers = [1, 2, 3];
6
7console.log(typeof name);
8console.log(typeof age);
9console.log(typeof isActive);
10console.log(typeof person);
11console.log(typeof numbers);

Output

Your output will appear here...

Remember:

null is a special case in JavaScript.
Arrays and functions are objects.
Use typeof to debug and understand your variables.