✨identity (proxy)
JS ⟩ object ⟩ built-in ⟩ Proxy ⟩ example ⟩ identity (proxy)
an (proxy) object that appears to have an infinite number of read-only properties, where each property value is its key, that is, identity[key] === key.
replit ⟩ identity (proxy)
// identity (Proxy)
let identity = new Proxy({}, {
// ------------------------------------
// handler methods, triggered when ...
// ------------------------------------
// accessing `identity[key]`
get(o, key, receiver) { return key; }, // identity[key] === key
// testing if `key in identity`
has(o, key) { return true; }, // always true
// iterating through own keys of `identity`
ownKeys(o) {
throw new RangeError("Infinite number of properties");
},
// accessing property descriptor of `identity[key]`
getOwnPropertyDescriptor(o, key) {
return {
value: key,
enumerable: false, // non-writable/non-configurable/non-enumerable
writable: false,
configurable: false
};
},
// setting `identity[key]`
set(o, key, value, receiver) { return false }, // cannot set
// deleting `identity[key]`
deleteProperty(o, key) { return false }, // cannot delete
// (re)defining properties of `identity`
defineProperty(o, key, desc) { return false }, // cannot (re)define
// testing if `identity` is extensible
isExtensible(o) { return false }, // always false
// getting prototype of `identity`
getPrototypeOf(o) { return null }, // no prototype
// setting prototype of `identity`
setPrototypeOf(o, proto) { return false }, // cannot set
});
// test identity
identity.x, // 'x'
identity.toString, // 'toString'
identity[0], // '0'
delete identity.x, // ⛔ [TypeError] 'deleteProperty' on proxy: trap returned falsish for property 'x'
identity.x = 1, // ⛔ [TypeError] 'set' on proxy: trap returned falsish for property 'x'
Object.keys(identity), // ⛔ [RangeError] Infinite number of properties
for (let p of identity);, // ⛔ [TypeError] identity is not iterableLast updated