I am working with a function that has its return type determined by the arguments provided.
const example = (flag: boolean): typeof flag extends true ? "yes" : "no" => {
if (flag === true) {
return "yes"
} else {
return "no"
}
}
Why am I getting the error message
Type '"yes"' is not assignable to type '"no"'.ts(2322)"yes"?
This issue is occurring in Typescript version 4.8.4.
To achieve this, you can utilize a technique known as function overloading, where you specify the potential inputs and outputs for the function.
function checkStatus(flag: true): "yes";
function checkStatus(flag: false): "no";
function checkStatus(flag: true | false): "yes" | "no" {
return flag === true ? "yes" : "no"
}
What is the reason for the TSC error?
In my opinion, it is necessary to explicitly declare the returned value.
const test = (flag: boolean): typeof flag extends true ? 'yes' : 'no' =>
(flag === true ? 'yes' : 'no') as typeof flag extends true ? 'yes' : 'no';
Alternatively, you can use generics:
const test = <T extends boolean>(flag: T): T extends true ? "yes" : "no" =>
(flag === true ? "yes" : "no") as T extends true ? "yes" : "no";
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