Javascript - Collection Revocable Proxy
Introduction
ES6 can create proxies that can be revoked.
Proxy.revocable() method is used to create a revocable proxy object.
It takes a handler and a target object and returns a newly created revocable proxy object.
A revocable proxy object has two properties: proxy and revoke.
const { proxy, revoke } = Proxy.revocable(target, handler);
where,
- proxy - A Proxy object created with new Proxy (target, handler) call
- revoke - A function with no argument to invalidate (switch off) the proxy.
If the revoke() function gets called, the proxy becomes unusable.
Any trap to a handler will throw a TypeError.
Once a proxy is revoked, it will remain revoked and can be garbage collected.
Subsequent calls of revoke have no further effect.
Demo
const restaurant = {
soda: 10, //from ww w .ja v a 2s . co m
beer: 5
};
const { proxy, revoke } = Proxy.revocable(restaurant, {});
console.log(proxy.soda); // 10
console.log(proxy.beer); // 5
revoke();
console.log(proxy.soda); // TypeError: Revoked
Result
Revocable Proxy can be useful to enhance the security of an object where if attempts to access a private property has been made, the proxy can be revoked.
We can modify the above example to enhance the privacy of beer property as follows:
Demo
const restaurant = {
soda: 10, //from w ww. j a v a2s. co m
beer: 5
};
const resthandler = {
get: function(target, property) {
if (property === "beer") {
revoke();
return undefined;
}
return target[property];
}
}
const { proxy, revoke } = Proxy.revocable(restaurant, resthandler);
console.log(proxy.soda); // 10
console.log(proxy.beer); // undefined
console.log(proxy.soda); // TypeError: Revoked
Result
Here, we are returning undefined and revoking the proxy if beer property is accessed, cutting off further calls to the target object via proxy.