Basic types in TypeScript

typescript-basic-types.ts

// See blog post at https://ketuma.com/lessons/typescript-basic-types

//Boolean
const isOdd: boolean = true
const isEven: boolean = false

//Number
const fibonacci: number = 34 //decimal
const color: number = 0xbada55 //hexadecimal
const adder: number = 0b1011 //binary
const chmod: number = 0o755 //octal

//String
const firstName: string = "John"
const lastName: string = 'Smith'
const fullName: string = `${ firstName } ${ lastName }` // John Smith

//Array
const fibonacci: number[] = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
const faang: Array<String> = ['Facebook', 'Amazon', 'Apple', 'Netflix', 'Google']

//Tuple
let streetName: [number, string] = [322, 'HighWay Dr.']
console.log(streetName[0]) // 322
console.log(streetName[1]) // HighWay Dr.
streetName = ['HighWay Dr.', 322] // Error

//Enum
enum StateTrinity { Loading, Success, Error }
const ajaxCall: StateTrinity = StateTrinity.Success
const enumName: string = StateTrinity[2]
console.log(enumName) // Displays 'Error'

//Any
let ajaxResponse: any = { x: 20, y: 30, z: 40}
ajaxResponse = 'This is an error'
ajaxResponse = true

const random: any[] = ['House', 24, 'Roof', {x: 1, y: 2}]

//Void
function logOutput(): void {
  const message: string = receiveValueFromApi()
  console.log(message)
}

//Null and Undefined
let salary: number | null = 345000
salary = null // This is valid because null is part of the type.

//Never
// Inferred return type is never
function divideByZero(num: number) {
  throw new Error('We cannot divide by zero')
}

//Object
function parseObject(obj: object | null): void {
  console.log(obj)
}

parseObject({x: 10, y: 20, z: 30}) // OK
parseObject(null) // OK
parseObject(322) // Error
parseObject(true) // Error