How do you keep only the function-valued properties of a type? type Methods = { [K in keyof T as T[K] extends Function ? K : never]: T[K]; };

Remapping a key to never drops the property from the result

as never makes the property's value type never

This code causes a compile error

TypeScript · Senior · Question 8 of 75

How do you keep only the function-valued properties of a type?

type Methods<T> = {
  [K in keyof T as T[K] extends Function ? K : never]: T[K];
};

✓Correct answer: Remapping a key to never drops the property from the result
2as never makes the property's value type never
3This code causes a compile error

Explanation

If the expression after as evaluates to never, the key is dropped. It's the standard technique for filtering keys by value type. Without as, you'd first compute the union of keys and then apply Pick.

How do you keep only the function-valued properties of a type?

Explanation

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