How to assert that a string can be used as an array index w/o converting/asserting it to/as a number?

Question

I have a string value, which I intend to use as an index of an array. I'm sure of this value and want to assert that it's a valid 'index value', w/o converting it to a number at runtime or asserting it's a number (b/c it's not a number).

So I have:

const inputEl = window.document.getElementById('foo') as HTMLInputElement;
//it's indeed a string, I'm sure of it and have no squirm because of it
const v = inputEl.value as string;
const a = ['foo',];
const result = a[v];

console.log(result);

Currently tsc throws

Element implicitly has an 'any' type because index expression is not of type 'number' (tsserver 7015)

I'd rather not do something like:

//just because it's not a number
const v = inputEl.value as unknown as number;

Is there a better way to do it? Thank you.

A string can't be used as an array index. Array indexes are always numbers. If you want to use a string as key, you should use an object. — user16540390
– user16540390, Commented Nov 12, 2023 at 19:58
@jabaa does it mean that I must convert it to a number at runtime, like const num = Number(v); — d.k
– d.k, Commented Nov 12, 2023 at 20:00
TypeScript expects numbers as keys. JavaScript allows strings and implicitly converts them. I would explicitly convert the strings, avoid the implicit conversion and solve this problem. — user16540390
– user16540390, Commented Nov 12, 2023 at 20:02

Bergi · Accepted Answer · 2023-11-12 20:46:55Z

1

Just don't use the input .value string. Use its .valueAsNumber.

answered Nov 12, 2023 at 20:46

Bergi

671k162 gold badges1k silver badges1.5k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to assert that a string can be used as an array index w/o converting/asserting it to/as a number?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related