Typescript object rest typings in argument

Question

I'm a bit new to Typescript, and I can do typings for 90% of my codebase. But when it comes to rest/spread operators, I am absolutely at a loss. I happened upon this today in our code (I did not write this) but I did figure out that it doesn't work:

interface searchClient {
  searchForValues({
    name,
    query,
    ...qp,
  }: {
    name: string;
    query: string;
    qp: QpInterface;  //???this part doesn't work
  }): Promise<any>;
 }

interface QpInterface {
  page?: number;
  hits?: number;
  attributes?: string;
}

It doesn't work because qp is designating the name of the key in the typing whereas what I want to type is the ...qp part. Every key/value pair in ...qp is typed by the QpInterface.

Here's a sample function call:

this.searchClient.searchForValues({
  name: 'title',
  query: 'little sheep',
  page: 5,
  hits: 2
});

I couldn't find much on this on the documentation. I've tried putting ...qp: QpInterface; and ...QpInterface; which didn't work. What is the best way to type ...qp in the argument?

artem · Accepted Answer · 2017-11-16 00:28:18Z

7

Until spread types are implemented in TypeScript, you can use intersection type for this:

interface searchClient {
  searchForValues({
    name,
    query,
    ...qp,
  }: {
    name: string;
    query: string;
  } 
    & QpInterface): Promise<any>;
 }

answered Nov 16, 2017 at 0:28

artem

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