Can I give a useful generic type to a function that copies an object with a key added or replaced with a new value?

I have written the following function:

function extend(obj, key, value) {
    return { ...obj, [key]: value }
}

Ideally, I'd like be able to use this function generically, with obj being an Object whose type will be known at the callsite, key being a string which is constant at the callsite, and value a value whose type is known at the callsite. obj might or might not already contain the key, and the old value associated with that key may or may not be of the same type as the new value.

I've looked through the Utility Types reference, but I can't see anything that would allow me to write a useful type for extend. Is this possible?

You need generics (read the whole page to understand what is going on here):

function extend<T extends object, Key extends PropertyKey, Value>(obj: T, key: Key, value: Value): T & Record<Key, Value> {
    return { ...obj, [key]: value } as T & Record<Key, Value>;
}

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