in keyof interface index signature

[ardalanamini]

Search Terms

typescript interface index signature keyof

Suggestion

Make in keyof accessible to interface index signature

Use Cases

Suppose I have a class which on construct adds some getters and setters to itself by the provided object interface

Examples

interface Base<T extends object = {}> {
  [K in keyof T]: T[K];

  [key: string]: any;
}

class Base<T extends object = {}> {
  constructor(item: T) {
    this.foo = item.foo;
  }
}

const base = new Base({ foo: "bar" });

base.foo; // string

base.bar; // any

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

[weswigham]

Duplicate of #13573