How to use a variable as string or object in TypeScript?

Question

I have a variable that can either be a string or object like this:

value?: string | { name: string, type: string }

Trying something below but I get a compile error:

console.log(value?.name || value)
console.log(value?.type)

How can use this variable if it can be either type?

1st you use value and in second console you are using track? — Seti
– Seti, Commented Feb 16, 2022 at 0:10

Mike Jerred · Accepted Answer · 2022-02-16 00:20:20Z

5

In this case you can do:

console.log(typeof value === 'string' ? value : value?.name)

Typescript can narrow the type using type-guards, see here for more details.

edited Feb 16, 2022 at 0:20

answered Feb 16, 2022 at 0:11

Mike Jerred

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Seti · Accepted Answer · 2022-02-16 00:17:20Z

4

So you have two options

console.log(typeof value === 'string' ? value : value.name);

But as you used ?: in definition for this value (allowing undefined) and as i think that console is only for simple example there

if (value === undefined) {
} else if (typeof value === 'string') {
} else {
}

Would be best.

This issue you found is mostly done because both values for value variable are objects and ts saw that the types are not compatible and asks you to narrow them by hand

answered Feb 16, 2022 at 0:17

Seti

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