JavaScript

How to know the type of a JS variable?

typeof operator

Data types

1. Primitive → store a single value

2. Non-primitive → store multiple and complex values

Primitive data types

1. String

2. Number

3. Bigint → above number limits

4. Boolean

5. Undefined → declared but not assigned

6. Null → Non-existent, invalid value

7. Symbol → ES6 anonymous, unique value

typeof of primitive types

typeof "John Doe" // Returns "string"
typeof 3.14 // Returns "number"
typeof true // Returns "boolean"
typeof 234567890123456789012345678901234567890n // Returns bigint
typeof undefined // Returns "undefined"
typeof null // Returns "object" (kind of a bug in JavaScript)
typeof Symbol('symbol') // Returns Symbol

Non-primitive types

1. Object → store collection of data

→ any data type that’s not primitive is an object in JS

Hoisting

default behavior where all var and function declarations are moved on top