How can I find the definition of a built-in type like `RegExpExecArray`?

November 21, 2022

In the following code, the variable x has the type RegExpExecArray | null (according to VSCode).

  const storeIdRegExp = /s(?<storeId>\d+)/u;
  const x = storeIdRegExp.exec(query);

How can I find the definition of RegExpExecArray? I couldn’t find it documented anywhere.

Note: I did find a couple of references in the TypeScript source code, particularly 1.0lib-noErrors.js and lib.es2018.regexp.d.ts (which I assume applies if the compilation target is ES2018+). But that wasn’t easy to find and I’m not 100% sure the union of these interfaces is the correct answer.

>Solution :

You should write

let x: RegExpExecArray

and then use the "Go to definition" command (ctrl+click)

Then the editor will show you all the pieces of its definition:

// lib.es2018.regexp.d.ts
interface RegExpExecArray {
    groups?: {
        [key: string]: string
    }
}
// lib.es2015.d.ts
interface RegExpExecArray extends Array<string> {
    /**
     * The index of the search at which the result was found.
     */
    index: number;
    /**
     * A copy of the search string.
     */
    input: string;
}