In JavaScript, how to get parameters of a function on a prototype chain in a constructor?

Tips for accessing function parameters on prototype chains in JavaScript

In JavaScript development, it is often necessary to process functions and their parameters on the prototype chain. This article discusses how to access the parameters of a method on a prototype chain indirectly in the constructor. Direct access is impossible because the prototype method is called only after the constructor is executed, and the execution time of the two is different.

Consider the following code structure:

 function abc(k) {
  this.val = k this.q; // this.q is not defined, there may be an error here}

abc.prototype.add = function(q) {
  return this.val q; // Use this.val and parameters q
};

In the abc constructor, the parameter q of the add method cannot be directly obtained. q is only available in the internal scope of the add method.

In order to access the parameters of add method indirectly in the abc constructor, we can use a property to store the parameter. Here is an improved implementation:

 function Abc(k) {
  this.val = k; // Fix: Avoid this.addParams = {}; // Used to store parameters of the add method}

Abc.prototype.add = function(q) {
  this.addParams = q; // Store parameter q to addParams property return this.val q;
};

var x = new Abc(1);
x.add(2);
console.log(x.addParams); // { name: 2 } // Here the output should be 2, not the object

In this example, we create an addParams property, and assign the parameter q to it in the add method. In this way, after calling the add method by Abc instance x , you can access the parameters passed to add method through x.addParams . It should be noted that in the original example, console.log(x.params) outputs an object, which is inconsistent with the code logic and has been corrected here. If the parameter of the add method is an object, the addParams property stores the object.

In this way, we cleverly achieve the purpose of indirectly accessing method parameters on the prototype chain in the constructor, avoiding the limitation of direct access, and implementing the transmission and access of parameters between different methods.

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