OverrideProperties marks all properties optional

[crizo23]

The resulting type has all properties optional. I don't think this is intended?

I used the example from the docs:

type Foo = {
	a: string
	b: string
}
type Bar = OverrideProperties<Foo, {b: number}>
//=> {a: string, b: number}

I'm on typescript 5.2.2 and see a and b optional in Bar:

type Bar = {
    a?: string;
    b?: number;
}

[sindresorhus]

// @jinta4020 @nidomiro

[crizo23]

Same issue with Merge

[henriqueinonhe]

It's caused by the strict option in your tsconfig.json not being set to true.

[crizo23]

It's caused by the strict option in your tsconfig.json not being set to true.

confirmed! Thanks for the update.

[crizo23]

I am confused though why this tsconfig setting would affect the types generated by type-fest? @henriqueinonhe Is there a quick/easy explanation? thanks

[henriqueinonhe]

It doesn't affect the types generated themselves, but rather how Typescript checks types.

The strict option, when enabled, turns on several behaviors that make type checking "stricter".

In this case, it's probably caused especfically by the strictNullChecks flag.

Right now I won't be able to pinpoint the exact reason why strictNullChecks = false causes the problem you encountered, but the thing is that when that flag is turned off, it basically "ignores" null and undefined, effectivelly changing how the type checking works.