Caller and callee usages in JS __js

Caller function Fun Caller returns the function object that calls fun, which is the execution environment for fun, and returns null if the execution environment for fun is window

function Fun () {
    console.log (Fun.caller)//must be written in fun, because caller is only valid during function execution
}
fun ();
The result is: null

One layer below.

function A () {
    fun ();
    function Fun () {
        console.log (Fun.caller)//must be written here in fun, because caller is only valid during function execution
    }
}
a ();

The result is: a function

In a layer of wrapping

function A () {
    B ();
    Function B () {
        fun ();
        function Fun () {
            console.log (Fun.caller)//must be written here in fun because caller is only valid during function execution
        }}
a ();

The result is: b function
callee This property is above the arguments of the function

function A () {
    console.log (Arguments.callee)
}
A ();
The result is the A function itself

The following is a classic factorial function

function sum (num) {
    if (num <= 1) {return
        1;
    } else{return
        num * (SUM (num-1)
    }}
Console.log (SUM (5))
/Result: 5*4*3*2*1=120

In order to avoid the function name modification causes the function internal error, changes writes below

function sum (num) {
    if (num <= 1) {return
        1;
    } else{return
        num * (Arguments.callee (num-1))
    }
console.log (SUM (5))
//Result: 5*4*3*2*1=120

Another use of callee

function A (num1,num2,num3) {
    console.log (arguments.length);//The argument length is 1
    console.log ( arguments.callee.length)//Line parameter length is 3
}