function types typescript code example

Example 1: typescript default parameter

// Default Parameters
sayHello(hello: string = 'hello') { 
    console.log(hello); 
}

sayHello(); // Prints 'hello'

sayHello('world'); // Prints 'world'

Example 2: typescript function as parameter

function createPerson(name: string, doAction: () => void): void {
  console.log(`Hi, my name is ${name}.`);
  doAction(); // doAction as a function parameter.
}

// Hi, my name is Bob.
// performs doAction which is waveHands function.
createPerson('Bob', waveHands());

Example 3: 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 4: typescript function

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

// Anonymous function
let myAdd = function (x: number, y: number): number {
  return x + y;
};

Example 5: types function typescript

interface Param {
    title: string;
    callback: function;
}

Example 6: types function typescript

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