如何在 TypeScript 中键入普通 object

Question

I wanna type a plain object of JavaScript, and write this:

interface PlainObject {
  [k: string]: any;
}

But I found:

type A = keyof PlainObject // string | number

interface PlainArray {
  [k: number]: any;
}

type B = keyof PlainArray // number

Question 1: Why this happens? Question 2: How can I type a plain object like { name: 'timi' }

Answer 1

This behavior is by design, the string index will mean the object is indexable by a string or a number . The docs say it best:

If you have a type with a string index signature, keyof T will be string | number string | number (and not just string, since in JavaScript you can access an object property either by using strings (object['42']) or numbers (object[42])). And T[string] is just the type of the index signature.

There is no way to have a type for which keyof will return just string . (There is the --keyofStringsOnly compiler option but that is there mostly for backward compatibility and should not be enabled on new code)