remove null or undefined from properties of a type

I need to declare a type such that removes the undefined from its property types.

Suppose we have:

type Type1{
  prop?: number;
}

type Type2{
  prop: number | undefined;
}

type Type3{
  prop: number;
}

I need to define a generic type called NoUndefinedField<T> such that NoUndefinedField<Type1> gives the same type as Type3 and the same type as NoUndefinedField<Type2>.

I tried this

type NoUndefinedField<T> = { [P in keyof T]: Exclude<T[P], null | undefined> };

But it only works for Type2.

Solution 1:

There is also now the NonNullable type built in:

type NonNullable<T> = Exclude<T, null | undefined>;  // Remove null and undefined from T

https://www.typescriptlang.org/docs/handbook/utility-types.html#nonnullablet

Solution 2:

Thanks to @artem, the solution is:

type NoUndefinedField<T> = { [P in keyof T]-?: NoUndefinedField<NonNullable<T[P]>> };

Notice the -? syntax in [P in keyof T]-? which removes optionality

Solution 3:

@DShook's answer is incorrect (or rather incomplete) because the OP is asking to remove null and undefined from the types properties, not from the type itself (a distinct difference).

While @Fartab's answer is correct, I'll add to it, as there is now the built-in Required type, and the solution can be re-written as:

type RequiredProperty<T> = { [P in keyof T]: Required<NonNullable<T[P]>>; };

This will map the types properties (not the type itself), and ensure that each one is neither; null or undefined.

An example of the difference between removing null and undefined from the type, versus removing them from a types properties (using the above RequiredProperty type):

type Props = {
  prop?: number | null;
};

type RequiredType = NonNullable<Props>; // { prop?: number | null }
type RequiredProps = RequiredProperty<Props>; // { prop: Required<number> } = { prop: number }

Solution 4:

Something in both @Fartab's and @tim.stasse's answers is messing up a property of type Date for me:

// both:
type NoUndefinedField<T> = {
  [P in keyof T]-?: NoUndefinedField<NonNullable<T[P]>>;
};
type NoUndefinedField<T> = {
  [P in keyof T]-?: NoUndefinedField<Exclude<T[P], null | undefined>>;
};
// throw:
Property '[Symbol.toPrimitive]' is missing in type 'NoUndefinedField<Date>' but required in type 'Date'.ts(2345)
// and
type NoUndefinedField<T> = { [P in keyof T]: Required<NonNullable<T[P]>> };
// throws:
Property '[Symbol.toPrimitive]' is missing in type 'Required<Date>' but required in type 'Date'.ts(2345)

I'm having success with this solution without recursion:

type NoUndefinedField<T> = {
  [P in keyof T]-?: Exclude<T[P], null | undefined>;
};

Solution 5:

Nowadays you can use Required to do exactly what you need:

Required<Type1>

That will result in all the fields becoming non-optional. More details can be found here