How to pass optional parameters while omitting some other optional parameters?

Question

Given the following signature:

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

How can I call the function error() not specifying the title parameter, but setting autoHideAfter to say 1000?

Answer 1

As specified in the documentation, use undefined:

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); 

Playground link.

Answer 2

Unfortunately there is nothing like this in TypeScript (more details here: https://github.com/Microsoft/TypeScript/issues/467)

But to get around this you can change your params to be an interface:

export interface IErrorParams {   message: string;   title?: string;   autoHideAfter?: number; }  export interface INotificationService {   error(params: IErrorParams); }  //then to call it: error({message: 'msg', autoHideAfter: 42});