getter与setter.md

Getter and Setter

A getter is a method that retrieves the value of a particular property, while a setter is a method that sets the value of a specific property.

Description

• Through getter and setter, interception operations for data retrieval and assignment can be implemented. When you want to monitor the change of a value, you can achieve this through getter and setter without having to find and modify every piece of code that operates this value.
• Sometimes it is necessary to allow access to properties that return dynamically calculated values or reflect the state of internal variables without the need for explicit method calls, which can be achieved using getter and setter.
• Although getter and setter can be combined to create a pseudo-property, it is not possible to bind getter and setter to a property that actually has a value.

Literal Declaration

You can directly declare get and set methods when creating objects through literals.

var obj  = {
    __x:1,
    get x(){
        console.log("Retrieval operation");
        return this.__x;
    },
    set x(v){
        console.log("Assignment operation, such as updating the view");
        this.__x=v;
    }
}
console.log(obj.x); // 1
obj.x = 11;
console.log(obj.x); // 11
/*
  Defining __x with a double underscore at the beginning indicates a property that is not intended to be accessed directly
  Of course, you can directly use obj.__x for property assignment and retrieval operations, but this would defeat the purpose of get and set
 */
/*
  In addition, as mentioned in the third point of the description, it is not possible to bind a getter and setter to a property that actually has a value, otherwise it will result in an infinite recursion and stack overflow, causing an exception
  var obj  = {
      x:1,
      get x(){
          return this.x;
      },
      set x(v){
          this.x=v;
      }
  }
  console.log(obj.x); // Uncaught RangeError: Maximum call stack size exceeded
/*

Object.defineProperty

Use Object.defineProperty() to precisely add or modify an object's properties.

var obj  = {
    __x:1
}
Object.defineProperty(obj, "x", {
    get: function(){
        console.log("Retrieval operation");
        return this.__x;
    },
    set: function(v){
        console.log("Assignment operation, such as updating the view");
        this.__x=v;
    }
});
console.log(obj.x); // 1
obj.x = 11;
console.log(obj.x); // 11

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