JavaScript learning tips: The difference between call and apply_javascript skills

1. call
call method
Call a method of an object to replace the current object with another object.
call([thisObj[,arg1[, arg2[, [,.argN]]]]])
Parameters
thisObj
Optional. The object that will be used as the current object.
arg1, arg2, , argN
Optional. A sequence of method parameters will be passed.
Description
The call method can be used to call a method instead of another object. The call method changes the object context of a function from the initial context to the new object specified by thisObj.
If no thisObj parameter is provided, the Global object is used as thisObj.
Simple example (function call):

Copy code The code is as follows:

function add(a,b)
{
alert(a b);
}
function sub(a,b)
{
alert(a-b);
}
add.call(sub,3,1);

In this example, it means to replace sub with add, add.call(sub,3,1) == add(3,1 ), so the running result is: alert(4); Complex example (method call):

Copy code The code is as follows:

function Class1()
{
this.name = "class1";
this.showNam = function()
{
alert(this.name );
}
}
function Class2()
{
this.name = "class2";
}
var c1 = new Class1();
var c2 = new Class2();
c1.showNam.call(c2);

Note that call means to put the method of c1 on c2 for execution. It turns out that c2 does not have showNam. () method, now put the showNam() method of c1 on c2 for execution, so this.name should be class2, and the result of execution is: alert ("class2");
Implement inheritance

Copy code The code is as follows:

function Class1()
{
this.showTxt = function(txt )
{
alert(txt);
}
}
function Class2()
{
Class1.call(this);
}
var c2 = new Class2();
c2.showTxt("cc");

In this way, Class2 inherits Class1. Class1.call(this) means using the Class1 object instead of this object. , then doesn’t Class2 have all the properties and methods of Class1? The c2 object can directly call the methods and properties of Class1. The execution result is: alert (“cc”);
Yes, that’s it, this This is how JavaScript simulates inheritance in object-oriented and can also implement multiple inheritance.

Multiple inheritance

Copy code The code is as follows:

function Class10()
{
this.showSub = function(a,b)
{
alert(a-b);
}
}
function Class11()
{
this.showAdd = function(a,b)
{
alert(a b);
}
}

function Class2()
{
Class10.call(this);
Class11.call(this);
}

It’s very simple, using two calls to achieve multiple inheritance
Of course, js There are other methods of inheritance, such as using the prototype chain. This is not within the scope of this article. I just explain the usage of call here
I mentioned call, and of course apply. These two methods basically mean the same thing
The difference The second parameter of call can be of any type, while the second parameter of apply must be an array

2. apply

for both apply and call The functions are the same, but the parameters are different.
The first parameter has the same meaning, but for the second parameter:
apply passes in a parameter array, that is, multiple parameters are combined into an array and passed in, and call is used as call. Parameters are passed in (starting with the second parameter).
For example, the corresponding apply writing method of func.call(func1,var1,var2,var3) is: func.apply(func1,[var1,var2,var3])

Tips (the code is elegant and its execution efficiency High)

Copy code The code is as follows:

alert(Math.max(5,8) ) //8
alert(Math.max(5,7,9,3,1,6)) //9

var arr=[5,7,9,1]
alert(Math.max.apply(null,arr));