Typescript error: Type 'undefined' is not assignable to type 'string'

Question

I've got the following function

this._list.addToFavs((<HTMLElement>event.currentTarget).dataset.code)

where addToFavs is defined as addtoFavs(currencyCode: string)

I'm getting the error "Type 'undefined' is not assignable to type 'string'" as dataset.code could in theory be 'undefined'. I know I can work around it by adding ! at the end, but I feel like it's kind of messy. I tried adding

if ((<HTMLElement>event.currentTarget).dataset.code == undefined) {
  throw Error('Code not set to details fav button')
}

but it doesn't stop the error. Is there any way around it besides defining currencyCode as string|undefined?

alper · Accepted Answer · 2023-11-18 20:14:11Z

1

Before invoking the function, you can check the existence of specific data attribute.

const code = event.currentTarget?.dataset?.code;
if (code) {
    this._list.addToFavs(code);
}

edited Nov 18, 2023 at 20:14

alper

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answered May 1, 2022 at 5:28

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