Typescript Tutorial Development Tutorials, Guides & Insights

type Readonly<T> = {
  readonly [K in keyof T]: T[K];
};

type PointReadonly = Readonly<Point>;

Conditional types provide a way to define types that depend on other types. This allows for more dynamic and context-sensitive type definitions.

type ID = string | number;

function printId(id: ID): void {
  console.log(id);
}

printId(101);
printId("abc123");

Unions let you define a variable that can hold more than one type:

"scripts": {
  "build": "tsc",
  "start": "node dist/index.js"
}

After conversion, it’s crucial to ensure that your application still functions correctly:

function add(a: number, b: number) {
  return a + b; // inferred return type is number
}

let numbers = [1, 2, 3]; // inferred as number[]

const handler = (event: MouseEvent) => {
  console.log(event.button); // inferred as MouseEvent
};

window.onclick = handler;