IARI

type NativeType = null | number | string | boolean | symbol | Function;
type InferDefault<P, T> = ((props: P) => T & {}) | (T extends NativeType ? T : never);

function getDefault<P, K extends keyof P>(defaults: DefaultProps<P>, k: K, injected?: DefaultProps<P>): InferDefault<P, P[K]> | undefined {
    return (p) => {
        const t: InferDefault<P, P[K]> | undefined = (injected && k in injected) ? injected[k] : defaults[k]
        if (typeof t === 'function') return t(p)
        return t
    }
}