Use of the Apply method in JS

1, the object of inheritance, the general practice is to replicate: Object.extend

The prototype.js is implemented in the following ways:

1  function       2 for in3destination[property] =           4    5     return6 }

In addition, there is a way, is: function.apply (of course, the use of Function.call is also possible)

The Apply method can hijack another object's method, inheriting another object's properties

Function.apply (Obj,args) method can receive two parameters

OBJ: This object will replace the This object in the function class

Args: This is an array, which is passed as a parameter to function (args-->arguments)

The Apply model code is as follows:

1<script>2 functionPerson (name,age) {//define a class, human3      This. name=name;//name4      This. age=age;//Age5      This. sayhello=function() {alert ("Hello")};6 } 7 functionPrint () {//display the properties of a class8      This. Funcname= "Print"; 9      This. show=function(){      Ten         varmsg=[]; One          for(varKeyinch  This){  A             if(typeof( This[key])! = "function"){ -Msg.push ([Key, ":", This[Key]]. Join ("")); -             } the         }  -Alert (Msg.join ("")); -     }; - }  + functionStudent (Name,age,grade,school) {//Student Class -Person.apply ( This, arguments); +Print.apply ( This, arguments); A      This. Grade=grade;//Grade at      This. School=school;//School - }  - varp1=NewPerson ("Jake", 10); - P1.sayhello (); - vars1=NewStudent ("Tom", 13, 6, "Tsinghua Primary School")); - s1.show (); in S1.sayhello (); - alert (s1.funcname); to</script>

The student class would not have had any method, but after person.apply (this,arguments),

He has the SayHello method and all the attributes of the person class.

The show () method is automatically obtained after print.apply (this,arguments)

2, using the parameter array of apply to improve

Function.apply () Tips for improving program performance

Let's start with the Math.max () function, the Math.max can be followed by any parameter, and finally the maximum value in all parameters is returned.

Like what
Alert (Math.max (5,8))//8
Alert (Math.max (5,7,9,3,1,6))//9

But in many cases, we need to find the largest element in the array.
var arr=[5,7,9,1]
Alert (Math.max (ARR))//This is not possible. It must be written like this.

function Getmax (arr) {
var arrlen=arr.length;
for (Var i=0,ret=arr[0];i<arrlen;i++) {
Ret=math.max (Ret,arr[i]);
}
return ret;
}

It's troublesome and inefficient to write. If you use apply, look at the code:
function GetMax2 (arr) {
Return Math.max.apply (Null,arr);
}
The two pieces of code achieve the same goal, but GETMAX2 is elegant, efficient, and much simpler.

Another example is the push method of the array.
var arr1=[1,3,4];
var arr2=[3,4,5];
If we want to expand the arr2 and then add one to the arr1, and finally let arr1=[1,3,4,3,4,5]
Arr1.push (ARR2) is obviously not going to work. Because doing so will get [1,3,4,[3,4,5]]

We can only use a loop to go to one push (or Arr1.concat (ARR2), but the Concat method does not change arr1 itself)
var arrlen=arr2.length
for (Var i=0;i<arrlen;i++) {
Arr1.push (Arr2[i]);
}

It's been so easy since I got the Apply
Array.prototype.push.apply (ARR1,ARR2)

Use of the Apply method in JS