There is a piece of code in TypeScript's document about Mapped Types which illustrates how to use mapped type to implement a proxy. It clearly defines what the type of a proxy for a value is, i.e. Proxy<T> and what the type of a proxified object is, i.e. Proxify<T>. However, the implementation of the proxify function is left empty. In order to strengthen my understanding of the mapped type, I decided to implement it.
type Proxy<T> = {
get(): T;
set(value: T): void;
};
type Proxify<T> = {
[K in keyof T]: Proxy<T[K]>;
};
function proxify<T extends object>(o: T): Proxify<T> {
const result = {} as Proxify<T>;
for (let key in o) {
let rawValue = o[key];
result[key] = {
get: () => rawValue,
set: (value) => {
rawValue = value;
},
};
}
return result;
}
let props = { rooms: 4 };
let proxifiedProps = proxify(props);
proxifiedProps.rooms.set(5);
console.log(proxifiedProps.rooms.get()); // output 5
As you see, it's not difficult however it can help learners like me to get a better understanding of the concept.
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