'string | 类型的参数 undefined' 不能分配给'string' 类型的参数。 typescript '严格'

Question

I am trying to replace an object using SDK, and typescript throws the following error with the 'strict' mode on,

const offer = client.offer(oldOfferDefinition!.id);
await offer.replace(newOfferDefinition);

error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'. Type 'undefined' is not assignable to type 'string'.

const offer = client.offer(oldOfferDefinition!.id);

I am sure that oldOfferDefinition has id and it has a value, how can i get rid of this compliation error?

Answer 1

If you are sure that it does, then throw an exception if it doesn't.

const id = oldOfferDefinition!.id;
if (typeof id === "undefined") {
    throw new Error("ID for old offer is undefined");
}
const offer = client.offer(id);

Since the runtime can't reach the line where you pass the value to offer if that value is undefined, then the TS compiler will be happy with it.

Answer 2

remove, mark form oldOfferDefinition, and encapsulte this to condition

if(oldOfferDefinition){
    const offer: string = client.offer(oldOfferDefinition.id);
    await offer.replace(newOfferDefinition);
}

but you should secure, that the result type of offer() function is defined as string