interface featureType<Props=any, State=any> {
initialState: State;
props: Props;
processState: (props: Props, state: State) => any;
}
const feature1Comp: featureType = {
initialState: { lastName: '' },
props: { firstName: 'eliav' },
processState: (props, state) => {
props; // type should be {firstName: string} but instead is any
},
};
why props type is not being inferred? what am I missing?
quick playground here(the URL is being cut so copy-paste the code)
(I post this question only because it takes too much time to find a solution for that issue and this is quite a common usage for typescript)
const feature1Comp = FeatureType<{ firstName: string}, any>
Treat generics as a kind of 'type functions'. If you don't provide the concrete types, defaults will be used, so TS assumes Props and State are typed as any.
Update: here is what will work with infering
interface Component<P,S> {
initialState: S,
props: P,
processState: (props: P, state: S) => any
}
function createComponent<P, S>(arg: Component<P, S>): Component<P, S> {
return arg;
}
const x = createComponent({
initialState: 'someValue',
props: { firstName: 'Elias' },
processState: (p, s) => {
console.log(p.firstName) // Works
console.log(p.lastName) // Error
}
})