A secure method for converting a key and a corresponding value into an object containing only that specific key/value pair

I need to implement a function called valueToObject that takes a key and a value as arguments and returns an object with that key and value pair, like this:

valueToObject('myKey', 3);
// should yield {myKey: 3}

I attempted to write the following code:

type Wrapped<K extends string, V> = {
  [P in K]: V;
};
function valueToObject<K extends string, V>(key: K, value: V): Wrapped<K, V> {
  return {[key]: value};
}

However, this code does not compile without casting the return value to any:

error TS2322: Type '{ [x: string]: V; }' is not assignable to type 'Wrapped<K, V>'.

How can I modify this function to ensure type safety?

Answer №1

When utilizing a computed property with a generic parameter, the type will be automatically inferred as { [name: string]: V }. This appears to be linked to an issue mentioned in this thread, where despite being marked as resolved, recent comments suggest it is still prevalent in version 2.9.

Edit Another related issue is currently open for Version 3.0 release, indicating a potential fix in the near future.

The only workaround at the moment is to use a type assertion:

function valueToObject<K extends string, V>(key: K, value: V): Wrapped<K, V> {
    return { [key]: value } as Wrapped<K, V>;
}
//OR
function valueToObject<K extends string, V>(key: K, value: V): Wrapped<K, V> {
    var result = {} as Wrapped<K, V>
    result[key] = value;
    return result;
}

I recommend raising this issue on GitHub or commenting on the existing thread to bring attention to this ongoing issue.

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