JS functions

function

Page statements are executed sequentially , Defining functions facilitates code encapsulation , You can deal with js Encapsulated in a function , Reduce code writing , Support multi page calling , You can also execute through events

Definition of function

Ordinary function

function Function name (){

Execute statement

}

call ： Function name ()

Functions with parameters

function Function name (a,b,c){

Execute statement

}

call ： Function name (1,2,3)

Function with return value

function Function name (a,b,c){

Execute statement

return a+b

}

call ：var v= Function name (1,2,3)

recursive ： Call yourself , Simulation cycle

function Function name (num){

if(num==1){

return 1

}

return Function name (num-1)

}

call ：var v= Function name (10)

for example ：function fun( num){

            if(num<=1){

                return 1

            }

            return num*fun(num-1)

        }

       var v=fun(6)

       console.log(v)

Js No overloading

Can be in the same scope , Define a function with the same name , But do different things ,js Can not be

for example ：function fun(a,b){

            console.log(" first ")

        }

        function fun(a,b,c){

            console.log(" the second ")

        }

        fun(1,2)

The second overwrites the first

Function declaration

1、 Function declaration

  for example ：function fun(a,b){// Function declaration

            console.log(" first ")

        }

fun()

2、 Function expression

for example ：var fun1=function(a,b){// Function expression

        console.log(" first ")

       }

 fun1()

3、 Anonymous functions Put in front and execute first

for example ：

(function(){

        console.log(" This is an anonymous function ")

 })()

Variable array ( Variable parameters )

be called arguments, It's like an array , Used to receive multiple parameter values under the function , Can only be used in functions , But you can't change it like an array

for example ： function fun(){

        console.log(arguments)

        console.log(arguments.length)//6

        console.log(arguments[2],arguments[4])//3 5

    }

    fun(1,2,3,4,5,6)

Be careful ：arguments Although similar to an array , But it's a fixed length , Unlike arrays, which are variable length , For the array operation function , Not available except for traversal , You can only change variables and values of variable arrays