TypeScript 기본

const car: string = 'bmw';
const age: number = 30;
const a: number[] = [1, 2, 3];
const a2: Array<number> = [1, 2, 3];

const week1: string[] = ['mon', 'tue', 'wed'];
const week2: Array<string> = ['mon', 'tue', 'wed']; // Generic

week1.push(1); // ERROR

let b: [string, number];

b = ['abc', 1];
b = [1, 'abc']; // ERROR

b[0].toLowerCase();
b[1].toLowerCase(); // ERROR

const n: null = null;
const u: undefined = undefined;

enum Os { // 보통 enum의 이름은 대문자로 시작한다.
  Window,
  Ios,
  Android,
}

let myComputer: Os;
myComputer = Os.Window;
myComputer = 'Window'; // ERROR
console.log(myComputer); // 0

// 숫자 열거형
enum Os {
  Window = 1,
  Ios,
  Android = 10,
}

console.log(Os.Window); // 1
console.log(Os.Ios); // 2
console.log(Os.Android); // 10

// 문자열 열거형
enum Os {
  Window = 'Window',
  Ios = 'Ios',
  Android = 'Android',
}

console.log(Os.Window); // Window
console.log(Os.Ios); // Ios
console.log(Os.Android); // Android

let str: any = 'hi';
let num: any = 12;
let arr: any = [1, 2];

let jkeObj: { name: string; age: number; hobbies: string[] } = {
  name: 'jke',
  age: 27,
  hobbies: ['Music', 'BasketBall'],
};

// Union
let unionType: number | string | number[] = 1;
unionType = 'jke';
unionType = 1;
unionType = [1, 2, 3];
// 이렇게 사용 시 타입스크립트의 의미가 사라지는 것이므로
// 추천되는 방법은 아니다.

let gender: 'M' | 'F' = 'M';
gender = 'F';
gender = 'T'; // error

function sayHello(): void {
  console.log('hello');
}

function showError(): never {
  throw new Error();
}

function infLoop(): never {
  while (true) {
    // Do Something ...
  }
}

let variable: unknown

variable = true // OK (boolean)
variable = 1 // OK (number)
variable = 'string' // OK (string)
variable = {} // OK (object)

let anyType: any = variable // OK
let booleanType: boolean = variable
// Error: Type 'unknown' is not assignable to type 'boolean'.(2322)
let numberType: number = variable
//  Error: Type 'unknown' is not assignable to type 'number'.(2322)
let stringType: string = variable
//  Error: Type 'unknown' is not assignable to type 'string'.(2322)
let objectType: object = variable
//  Error: Type 'unknown' is not assignable to type 'object'.(2322)

let age:3 = 3;
age = 5; // Error

let name:"jke" = "jke";
name = "jkejkejke" // Error

// literal type으로 추론
const age = 1;
const name = "jke"

const numbers = [1,2,3] // number[]로 추론
const numbers = [1,2,3] as const // [1,2,3]

const obj = {x:1, y:2} // {x:number, y:number}
const obj = {x:1, y:2} as const // {x:1, y:2}

function map(array:number[], callback:(...args:any[]) => any;) {
	const result = [];

	for(const element of array){
		result.push(callback(element));
	};

	return result;
}

map([1,2,3,4], x => x + 1); // Good
map(["hello", "world"], x => x.toUpperCase()); 
// Type 'string' is not assignable to type 'number'.

function map<T>(array:T[], callback:(...args:any[]) => any;) {
	const result = [];

	for(const element of array){
		result.push(callback(element));
	};

	return result;
}

map<number>([1,2,3,4], x => x + 1);
map<string>(["hello", "world"], x => x.toUpperCase());

type People = {name: string, age:number, gender:"male" | "female", hobby:string};

type KeyOfPeople = keyof People; // name | age | gender | hobby

const key:KeyOfPeople = 'name';
const key2:KeyOfPeople = 'email'; // Error

const jke = {
	name:"jke",
	age:27,
	gender:"male",
	hobby:"basketball"
};

type People = typeof jke;
/* 
	{
	  name: string;
	  age: number;
	  gender: string;
	  hobby: string;
	}
*/


// keyof와 typeof 결합
type KeyOfPeople = keyof typeof jke;
// name | age | gender | hobby

function toUpper(arg:string | number){
	arg.toUpperCase() // Error
	/*
		Property 'toUpperCase' does not exist on type 'string | number'.
	  Property 'toUpperCase' does not exist on type 'number'.
	*/
}

// narrowing
function toUpper(arg:string | number){
	if(typeof arg === "string"){
		arg.toUpperCase() // OK!
	}
}

function addFive(num?:number){
	return num + 5; // Error
	/*
		(parameter) num: number | undefined
		Object is possibly 'undefined'.
	*/
}


// narrowing 
function addFive(num?:number){
	if(num){
		return num + 5
	} else {
		throw new Error("Argument num is not a number")
	}
}

// 예시1
type numOrStr = string | number;
let data: numOrStr = 1;
data = '1';
let typeArr: numOrStr[] = [1, '2', 3, '4'];

// 예시 2
type grade = 'A' | 'B' | 'C' | 'D' | 'E';
const jkeGrade: grade = 'A';

interface User {
  name: string;
  id: string;
  age: number;
  isMember: boolean;
}

const jkeInfo: User = {
  name: 'jke',
  id: 'j56237',
  age: 27,
  isMember: true,
};