any 혹은 unkown 으로 선언해두고 참조할 때 타입을 assert함 (type 덮어쓰기)
// (1) as
let someValue: unknown = "this is a string";
let strLength: number = (someValue as string).length; // (*)
// (2) angle-bracket
let someValue: unknown = "this is a string";
let strLength: number = (<string>someValue).length; // (*)
하나 이상의 타입을 사용할 때 (more flexible)
function combine(input1: number | string, input2: number | string) {// (*)
let result;
if(typeof input1 === 'number' && typeof input2 === 'number') { // runtime type check
return input1 + input2;
} else {
return input1.toString() + input2.toString();
}
return result;
}
const combineAge = combine(21, 30);
const combineName = combine('Suyeon', 'Hanna');
It allows an exact value which a string, number, or boolean must have.
// string
function createElement(tagName: "img"): HTMLImageElement;
function createElement(tagName: "input"): HTMLInputElement;
function(reslut: 'img' | 'text') {
if(result === 'text') {
// ...
} else {
// ...
}
}
// number
interface MapConfig {
tileSize: 8 | 16 | 32;
}
setupMap({ tileSize: 16 });
// boolean
interface ValidationSuccess {
isValid: true;
};
Reusable custom type set.
type pet = 'cat' | 'dog';
type Combinable = string | number;
function combine(input1: Combinable, input2: Combinable){...}