Apply & Call

One. Significance

Function.apply (Obj,args)

Obj replaces function in this object

Args passed as a parameter to function

Two. Instance

1. obj in place of the This object in function

1     function f () {2          alert (this. Y); 3     }4      var obj = {x:1,y:2}; 5      F.call (obj);         // 3

2. API Application

Math.max (Param1,param2,param3 ...): Implementation gets the largest item in the array

Problem: Max does not support array parameters

Solution: According to the characteristics of apply to solve

var max=math.max.apply (null, array)

This block in the call when the first parameter gave a null, this is because there is no object to call this method, I just need to use this method to help me to calculate the return of the results on the line,

So directly passed a null past. Undefine is an undefined object, NULL is a defined object, but without an instance, it can be understood that NULL is the defined of obj.

3. Inheritance

1 /*Define a human*/2     functionPerson (Name,age)3     {4          This. name=name;5          This. age=Age ;6     }7     /*define a student class*/8 functionstudent (Name,age,grade)9     {TenPerson.apply ( This, arguments); One          This. grade=grade; A     } -     //Create a Student class -     varStudent=NewStudent ("Qian", 21, "first Grade")); the     //Test -Alert ("Name:" +student.name+ "\ n" + "Age:" +student.age+ "\ n" + "Grade:" +student.grade); -     //You can see the test results Name:qian age:21 Grade: First grade -     //I did not assign a value to the name and age attribute in the student class, why is there the value of these two properties, this is the magic of apply.