JavaScript class and inheritance: prototype attribute

We have used prototype property simulation class and inheritance implementation in Chapter 1. The prototype attribute is essentially a JavaScript Object. Each function has a default prototype attribute.

If this function is used to create a custom object, we call it a constructor. For example, the following simple scenario:

 
 

  
  
// Constructor 
  
  
Function Person (name ){
  
  
This. Name = name;
  
  
}
  
  
// Define the prototype of Person. attributes in the prototype can be referenced by custom objects. 
  
  
Person. prototype = {
  
  
GetName: function (){
  
  
Return This. Name;
  
  
}
  
  
}
  
  
Var zhang =NewPerson ("ZhangSan");
  
  
Console. log (zhang. getName ());// "ZhangSan" 
 
 

As an analogy, we consider the JavaScript data type-String), Number), Array), Object), Date) and so on. We have reason to believe that these types are implemented as constructors in JavaScript, such:

 
 

  
  
// Define the constructor of the array as a predefined type of JavaScript 
  
  
Function Array (){
  
  
//... 
  
  
}
  
  
 
  
  
// Initialize an array instance 
  
  
Var arr1 =NewArray (1,56,34,12);
  
  
// However, we prefer the following syntax definition: 
  
  
Var arr2 = [1,56,34,12];
 
 

At the same time, many methods for Array operations, such as concat, join, and push, should also be defined in the prototype attribute.

In fact, it is understandable that all the inherent Data Types in JavaScript have the read-only prototype attribute: Because if the prototype attribute of these types is modified, the predefined methods will disappear ), however, we can add our own extension methods to it.

 
 

  
  
// Extend a method for obtaining the minimum value to the Array of the inherent JavaScript type. 
  
  
Array. prototype. min = function (){
  
  
Var min =This[0];
  
  
For(Var I =1; I <This. Length; I ++ ){
  
  
If(This[I] <min ){
  
  
Min =This[I];
  
  
}
  
  
}
  
  
ReturnMin;
  
  
};
  
  
 
  
  
// Call the min Method on any Array instance 
  
  
Console. log ([1,56,34,12]. Min ());// 1 
 
 

Note: There is a trap. After adding an extension method to the Array prototype, this extension method will also be recycled when the for-in loop Array is used.

The following code illustrates this assumption that the min method has been extended to the Array prototype ):

 
 

  
  
var arr = [1, 56, 34, 12];  
  
  
var total = 0;  
  
  
for (var i in arr) {  
  
  
    total += parseInt(arr[i], 10);  
  
  
}  
  
  
console.log(total);   // NaN 
 
 

The solution is also simple:

 
 

  
  
var arr = [1, 56, 34, 12];  
  
  
var total = 0;  
  
  
for (var i in arr) {  
  
  
    if (arr.hasOwnProperty(i)) {  
  
  
        total += parseInt(arr[i], 10);  
  
  
    }  
  
  
}  
  
  
console.log(total);   // 103 
 
 

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5. Code Implementation of the JavaScript asynchronous call framework