32 lines
667 B
Markdown
32 lines
667 B
Markdown
# 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:
|
|
|
|
```js
|
|
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"
|
|
*/!*
|
|
```
|