JavaScript Reflection Learning Skills

Directory 1, Preface 2, Interface 3, Simple Example 4, Conclusion

1. Preface

According to MDN official website explanation: Reflect Is a built-in object that provides interception JavaScript The method of operation. These methods are the same as those of proxy handlers (en-US). Reflect Is not a function object, so it is not constructible.

So what exactly is it? According to the above file, you will find that it and Proxy Extremely similar, they all get the information of the execution function itself. The main difference is that all the function object attributes are too complex, and the extra addition may lead to unreasonable program behavior, so the extension Reflect Function to deal specifically with function object processing, such as calling methods, constructing objects, obtaining or setting properties, and other related operations.

2. Interface

Reflect All the methods in it are static methods, and there is no need to construct or instantiate it.

Reflect.apply ( target , thisArgument , argumentsList ), call a function and pass in an array as the call parameter. And JavaScript 0 The function is similar. JavaScript 1 ( target , JavaScript 3 ) Performs an new operation on the constructor, which is equivalent to executing the JavaScript 4 (... args). JavaScript 5 ( target , JavaScript 7 , JavaScript 8 ) and JavaScript 9 Similar. If the setting is successful, it will return Reflect 0 Reflect 1 As a function Reflect 2 Operator, which is equivalent to executing the Reflect 3 . Reflect 4 Gets the value of a property on an object, similar to Reflect 5 . Reflect 6 Similar to Reflect 7 . Returns the corresponding property descriptor if the property exists in the object, otherwise it returns Reflect 8 . Reflect 9 Similar to Proxy 0 . Proxy 1 Determines whether an attribute exists in 1 object, and Proxy 2 Operator functions exactly the same. Reflect.isExtensible(target) Similar to Object.isExtensible() . Reflect.ownKeys(target) Returns an array containing all its own attributes (excluding inherited attributes). (Similar to Object.keys() , but will not be affected by enumerable Influence). Reflect.preventExtensions(target) Similar to Object.preventExtensions() . Returns 1 Boolean . Reflect.set(target, propertyKey, value[, receiver\]) A function that assigns a value to a property. Returns 1 Boole an, if the update is successful, returns true . Reflect.setPrototypeOf(target, prototype) The function that sets the prototype of the object. Returns 1 Boolean If the update is successful, return the Reflect 0 .

3. Simple examples

For example, there is a function now:

class Person {
  constructor(firstName, lastName) {
    this.firstName = firstName
    this.lastName = lastName
  }
  get getName() {
    return this.firstName + ' ' + this.lastName
  }
}

Normal use only needs to be instantiated:

const person = new Person('Jaxson', 'Wang')
console.log(person.getName) // Jaxson Wang

You can use the Reflect. construct () method to create objects:

const person = Reflect.construct(Person, ['Jaxson', 'Wang'])
console.log(person) // Jaxson Wang

4. Conclusion

Reflect objects are often used with Proxy proxies for three reasons:

Reflect All static methods provided by the Proxy The second handle The parametric method is one model and one sample. Reflect 0 The return value required by the method is exactly the Reflect 1 Adj. Reflect 2 Method, it can be used naturally, and it is more convenient and accurate than direct object assignment/retrieval. Reflect 3 Parameters are irreplaceable.