Mapped Types: removing optional modifier

In Typescript 2.8 you can explicitly eliminate the modifier:

type Foo2 = {
  [P in keyof Foo]-?: number;
}

Or use the Required type that is built into newer versions.

If you are using an older version you can use this workaround:

type Helper<T, TNames extends string> = { [P in TNames]: (T & { [name: string]: never })[P] };
type Foo3 = Helper<Foo, keyof Foo>;

You can use Required<T> as an alternative to -?

interface Foo {
  one?: string;
  two?: string;
}

type Foo2 = {
  [P in keyof Required<Foo>]: number;
};

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