typescript optional paramters code example

Example 1: How to pass optional parameters while omitting some other optional parameters?

export interface INotificationService {
    error(message: string, title?: string, autoHideAfter? : number);
}

class X {
    error(message: string, title?: string, autoHideAfter?: number) {
        console.log(message, title, autoHideAfter);
    }
}

new X().error("hi there", undefined, 1000);

Example 2: typescript annotate return type

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