The call apply in JS

In JavaScript oop, we often define this:

function Cat () {
}
cat.prototype={
Food: "Fish",
Say:function () {
Alert ("I Love" +this.food);
}
}


var blackcat = new Cat;
Blackcat.say ();

But if we have an object Whitedog = {food: "Bone"}, we do not want to redefine it say method, then we can use call or Apply with Blackcat say method: BlackCat.say.call (Whitedog );

So, you can see that call and apply are meant to change this dynamically, and when an object does not have a method, but the others, we can use call or apply to manipulate other objects.

The DOM node chosen by document.getElementsByTagName is a type of array that is similar to array. It cannot apply methods such as Push,pop under the array. We can do this by:
var domnodes = Array.prototype.slice.call (document.getElementsByTagName ("*"));
This allows the domnodes to apply all the methods under the array.

1.call ()

Syntax: Obj1.call (obj2[,param1,param2,...])
Definition: Use Obj2 object instead of Obj1, call obj1 method. The obj1 will be applied to the OBJ2.
Description: The call method can be used to invoke a method in place of another object. The call method can change the object context of a function from the initial context to a new object specified by Obj2. If the OBJ2 parameter is not provided, then the Global object is used as the obj2.

2.apply ()

Syntax: Obj1.call (Obj2[,arrarg])
Definition: Use Obj2 object instead of Obj1, call obj1 method. The obj1 will be applied to the OBJ2.
Note: Call () is the same as apply (), but call () can receive parameters of any type, and apply () can only receive array parameters.

3. Basic usage [JavaScript]View PlainCopy

2. function Add (A, b) {
4. return a+b;
6. }
8. function sub (c,d) {
10. return c-d;
12. }
14. function result () {
16. this.addvalue = null;
18. this.subvalue = null;
20. this.showresult=function () {
22. Alert (this.addvalue);
24. Alert (this.subvalue);
26. }
28. }
30. var r = new result ();
32. R.addvalue = Add.call (sub,4,2); //6, apply the Add method to the sub, which is the pointer to the sub that points to the Add method
34. R.subvalue = Sub.call (add,4,2); //2, replacing the sub object with the Add object, and invoking the method of the Sub object
36. R.showresult (); //In JS The function is also a functions object, the function name is the object reference

4. Inheritance Features [JavaScript]View PlainCopy

2. function Add (A, b) {
4. return a+b;
6. }
8. function sub (c,d) {
10. return c-d;
12. }
14. function result () {
16. this.addvalue = null;
18. this.subvalue = null;
20. this.showresult=function () {
22. Alert (this.addvalue);
24. Alert (this.subvalue);
26. }
28. }
30. var r = new result ();
32. R.addvalue = Add.call (r,4,2); //6,r inherit all the attributes of the Add function
34. R.subvalue = Sub.call (r,4,2); //2,r all features of the integrated sub function
36. R.showresult ();

The call apply in JS