Reflect is a built-in object in JavaScript that provides reflection operations, and Proxy is a proxy mechanism for intercepting and customizing object operations. 1. Reflect provides unified and reasonable object operation methods, such as Reflect.get and Reflect.set, which replaces old APIs with clearer and more reliable; 2. Proxy creates an object proxy to implement data binding, access control and other functions, such as Vue.js' responsive system; 3. The combination of the two can simplify code logic, maintain behavioral standards, and facilitate expansion. The Reflect method is called by default to implement basic operations; 4. When using it, you need to pay attention to performance impact, compatibility and this pointing problem to avoid abuse. Mastering them can help develop efficient frameworks and in-depth understanding of language mechanisms.

Reflect and Proxy of JavaScript are two very powerful features in the language, and they together form the reflection (Reflection) API of JavaScript. Simply put, Reflect provides a set of static methods for manipulating objects, while Proxy allows you to intercept and customize basic operations on objects. Use these two together to implement advanced functions such as data binding, logging, verification, etc.

What is Reflect?

Reflect is not a constructor, but a built-in object, which provides a series of methods related to object operations. Most of these methods are similar to the same name method on Object, but the design is more consistent and the return value is more reasonable.

For example:

• Reflect.get(target, key) is similar to Object.getOwnPropertyDescriptor or directly access properties, but it handles traps better.
• Reflect.set(target, key, value) When setting the property, a boolean value will be returned to indicate whether it is successful, rather than throwing an exception like Object.defineProperty .

Commonly used scenarios:

• How to call in Proxy as the default behavior
• Replace some old-fashioned APIs, such as delete obj[key] can be written as Reflect.deleteProperty(obj, key)
• Handle object operation failures more clearly

What is Proxy? What's the use?

Proxy is used to create an object's proxy, which allows you to intercept and customize various basic operations of the object. You can understand it as a "middleman", and all operations on the target object can be controlled through this middleman.

 const handler = {
  get(target, key) {
    console.log(`${key}` accessed);
    return Reflect.get(target, key);
  }
};

const obj = { name: "Alice" };
const proxy = new Proxy(obj, handler);

console.log(proxy.name); // Output: accessed name, and then output Alice

Common Proxy usage scenarios:

• Data-binding or responsive systems (such as Vue.js)
• Intercept and verification of attribute access/settings
• Implement immutable objects or read-only views
• Logging, performance monitoring

Advantages of Reflect Proxy Use

When you use Reflect in Proxy's handler, the two work very well. Because the standard behavior provided by Reflect can be implemented directly as the default, you don't have to deal with each situation manually.

Advantages include:

• Concise code: Using the Reflect method can avoid duplicate logic
• Behavioral Standard: Reflect's method is consistent with the internal operations of the JS engine
• Easy to scale: You can flexibly decide whether to continue to perform default behavior in intercept logic

For example:

 const handler = {
  get(target, key, receiver) {
    if (key in target) {
      console.log(`get attribute ${key}`);
      return Reflect.get(target, key, receiver);
    } else {
      throw new Error(`Property ${key} does not exist`);
    }
  }
};

In this example, we judge whether the attribute exists and use Reflect to complete the standard attribute acquisition behavior when it exists.

Common misunderstandings and precautions

Although Reflect and Proxy are powerful, there are some places that are easy to get stuck in:

• Don't abuse Proxy : Overuse can lead to performance degradation, especially in high-frequency access scenarios.
• Reflect is not omnipotent : some operations cannot be completely overwritten, such as new expressions require construct trap.
• Note the pointing problem of this : when calling a method in Proxy, this may not be the expected object and needs to be corrected with receiver parameter.
• Compatibility Considerations : Proxy and Reflect are ES6 features that may not be supported in older browsers.

Basically that's it. Reflect and Proxy are very useful tools in modern JavaScript development, especially when building frameworks or libraries. Mastering them will not only help you write more elegant code, but will also deepen your understanding of language mechanisms.

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