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Error on reading non-existent property

Usually, an attempt to read a non-existent property returns undefined.

Create a proxy that throws an error for an attempt to read of a non-existent property instead.

That can help to detect programming mistakes early.

Write a function wrap(target) that takes an object target and return a proxy that adds this functionality aspect.

That’s how it should work:

let user = { name: "John" }; function wrap(target) { return new Proxy(target, { /* your code */ }); } user = wrap(user); alert(user.name); // John alert(user.age); // ReferenceError: Property doesn't exist: "age"
let user = { name: "John" }; function wrap(target) { return new Proxy(target, { get(target, prop, receiver) { if (prop in target) { return Reflect.get(target, prop, receiver); } else { throw new ReferenceError(`Property doesn't exist: "${prop}"`) } } }); } user = wrap(user); alert(user.name); // John alert(user.age); // ReferenceError: Property doesn't exist: "age"