Index signature for iteration in typescript

Question

We can all see that this code is valid javascript:

const myObj = {
  foo: "string",
  bar: 123,
  baz: "important stuff"
};

['foo', 'bar'].forEach((key) => {
  delete myObj[key];
});

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ foo: string; bar: number; baz: string; }'. No index signature with a parameter of type 'string' was found on type '{ foo: string; bar: number; baz: string; }'.

So what's the best way of doing this TypeScript compatible?

http://www.typescriptlang.org/play/#code/MYewdgzgLgBAtgTwPICMBWMC8MDeBYAKBhgDMQQAuGAImgCcBLMAc2oBpDiUBDOqgRgBMAZg5EYPAF5VqDOAAcQdKNzCxoAVxIlqhAL4BuQoQAUAbQDkZEBbYwLPOhYC6ASgB0ZOgFFuwABYmJgDWAKYIrlgAfLicMAAmoQA2oVCh8MjoZmEIzkYEeq75QA — MrMamen, Oct 23 '19 at 11:34
This is similar to https://stackoverflow.com/q/13315131/990642 — josephdpurcell, Aug 19 '22 at 15:52

JeromeBu · Accepted Answer · 2019-10-23T15:47:19.717

1

Try typing your array :

const myObj = {
  foo: "string",
  bar: 123,
  baz: "important stuff"
};

const myArray: (keyof typeof myObj)[] = ['foo', 'bar']

myArray.forEach(...)

edited Oct 23 '19 at 15:47

answered Oct 23 '19 at 11:32

JeromeBu

1,099
7
13

score 0 · Answer 2 · answered Oct 23 '19 at 11:27

0

One workaround is:

(['foo', 'bar'] as (keyof typeof myObj)[]).forEach((key) => {
  delete myObj[key];
});

But it does not prevent typing errors in the array-strings.

answered Oct 23 '19 at 11:27

MrMamen

359
2
14

Index signature for iteration in typescript

2 Answers2