Type system

Primitive/Value types

• string
• number
• boolean
• undefined
• null

undefined is a value type that has unique value undefined. null is not a type. typeof null returns 'object'

Reference types

• Object
• Function

Anonymous object

JavaScript does not have strongly typed system, any composed type can be described as

let person = {
    name: 'John',
    age: 18
}

All members except functions are called properties of an object. There are two ways to access properties.

• let name = person.name;
• let name = person['name'];

Just like a built-in indexer, JavaScript object has keys that can be used to get the value of corresponding property with the same name.

Array

Array in JavaScript is object

typeof [] === 'object' // true

Function

Boring...

Falsy values

• false
• undefined
• null
• 0
• '' (empty string)
• NaN

Default value

Default value and type of a JavaScript variable is undefined.

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

Bitwise Operator

8 bits integer for example:

// 1 = 00000001
// 2 = 00000010
// or = 00000011
// and = 00000000
console.log(1 | 2); // 3
console.log(1 & 2); // 0

| compares each digit by 1 as true, 0 as false, to tell the final result.