typescript define type of function code example

Example 1: types function typescript

interface Safer_Easy_Fix {
    title: string;
    callback: () => void;
}
interface Alternate_Syntax_4_Safer_Easy_Fix {
    title: string;
    callback(): void;
}

Example 2: typescript function type

// define your parameter's type inside the parenthesis
// define your return type after the parenthesis

function sayHello(name: string): string  {
  console.log(`Hello, ${name}`!);
}

sayHello('Bob'); // Hello, Bob!

Example 3: typescript function type

interface Date {
  toString(): string;
  setTime(time: number): number;
  // ...
}

Example 4: types function typescript

interface Easy_Fix_Solution {
    title: string;
    callback: Function;
}

Example 5: types function typescript

interface Alternate_Syntax_4_Advanced {
    title: string;
    callback<T extends unknown[], R = unknown>(...args?: T): R;
}

Example 6: typescript annotate return type

function add(x: number, y: number): number {
  return x + y;
}