Htykuut

This code properly flagged in TS:

<MyComponent nonexistentProp="foo" />

This code is not:

<MyComponent { ...{ nonexistentProp: "foo" }} />

It seems trivial for TS to check that improper props are not getting passed in - how can we enable this checking to ensure that we're passing in the expected props?

I suspect this type checking is subject to the same constraints as regular TypeScript code:

interface Contract {

  a: string;

}



const allowed: Contract = {

  a: "bc",

};



const notAllowed: Contract = {

  a: "bc",

  b: "dc",

};



const aboutToBeAllowed = {

  a: "bc",

  b: "dc",

};



const alsoAllowed: Contract = aboutToBeAllowed;

The problem shown here is that TypeScript has it's limitations, in that it's a structural type system.

It is only able to enforce the constraints that us humans think it should be doing in all cases during an object literal assignment (see notAllowed assignment).

The alsoAllowed case is essentially the same as the notAllowed variant, but it works. This is because the anonymous object satisfies the Contract constraints.

Similarly, in your TSX example, this is essentially the same behavior as regular TypeScript:

interface Props { a: string; };

const MyComponent: React.SFC<Props> = (props) => <div />;



const myCompOk1 = <MyComponent a="ab" />;



const myCompBad1 = <MyComponent a="ab" b="cd" />;



const anonPropsNoExtra = { a: "bc" };

const myCompOk2 = <MyComponent {...anonPropsNoExtra} />;



const anonPropsWithExtra = { a: "bc", b: "cd" };

const myCompOk3 = <MyComponent {...anonPropsWithExtra} />;

I don't believe it's possible for it to enforce it the way you're looking for