const target = {};
const handler = {
set(obj, prop, value) {
if (typeof value !== 'number') {
throw new TypeError('Value must be a number');
}
return Reflect.set(obj, prop, value);
}
};
const proxy = new Proxy(target, handler);
try {
proxy.x = 'hello';
} catch (e) {
console.log(e.message);
}
console.log(target.x); 