Proxy and Reflect Article — Arrow Functions or `this` in Class constructor

還沒有人認領這個 Issue。

**Source:** https://javascript.info/proxy
**Date Accessed:** 1 March 2022

A serious limitation in ES6 Proxy is the inability to proxy internal use of the `this` context inside a class. In the password example, if we use a class, then the differences in behaviour from using an arrow function vs a method is clear:

```ts

class User {

name = "John";
_password = "***";

checkPassword(value: string) {
return value === this._password;
}

checkPassword2 = (value: string) => {
return value === this._password;
}
};

const user = new Proxy(new User(), {

get(target: any, prop: string) {

if (prop.startsWith('_')) {
throw new Error("Access denied");
}
let value = target[prop];

// Commenting out the workaround
return value; // (typeof value === 'function') ? value.bind(target) : value; // (*)
},
});

console.log(user.checkPassword2('***')); // Arrow function works without the workaround because `this` is the internal context
console.log(user.checkPassword('***')); // Method fails with `Access denied` as expected

```

The point here is that if your class passes `this` somewhere in the constructor then that `this` cannot be proxied. This is a significant limitation of Proxy and should probably be mentioned in the article.

A good write up BTW.

Thanks

從 https://javascript.info/proxy 上的 Proxy 文章開始，並結合回報中 class 和 arrow function 的行為檢視密碼範例。更新文章，說明涉及內部使用 this 和透過 Proxy 存取的限制；當這項區別以及替代方案的背景獲得準確記錄時，即視為完成。

由索引模型根據 Issue 內容生成。