Understanding js-arguments

Construct an Array like yourself
The main points of the array-like structure:
1. The elements are array-type indexes
2. They have the length attribute

Js code

var test3 = {  
    0 : 10,  
    1 : function(){  
        return this[0];  
    },  
    length:2  
}  
console.log(Array.prototype.slice.call(test3));//打印[10, function()]

The function parameter arguments are array-like, but not arrays. (arguments are objects)
If you want to convert it to a real array, you can
var slice = [].slice;
slice.call(arguments);
You can also: Aarray.prototype.slice.call(arguments);

Js code

var o = {  
    name:"javascript"  
};  
var f1 = function(){  
    return 2;  
}  
var foo = function(a,b,c){  
    console.log(arguments, typeof arguments, $.type(arguments), typeof arguments.push);  
    //[100, function(), Object { name="javascript"}] object object undefined  
  
    //尽管arguments不是数组，但仍可以通过for循环取出每一个元素  
    for (var i in arguments ){  
        console.log(arguments[i]);  
    }  
    /*打印 
        100 
        function() 
        Object { name="javascript"} 
    */  
  
    //现在让数组的slice运行在arguments的context中，参数为0，则将arguments转成了数组，（arguments本身没变）  
    var ret = Array.prototype.slice.call(arguments);  
  
    console.log(ret, typeof ret, $.type(ret), typeof ret.push);  
    //[100, function(), Object { name="javascript"}] object array function  
}  
foo(100,f1,o);

Basic introduction
When js makes a function call, in addition to the specified parameters, it also creates an implicit object - arguments.
1. Arguments can be evaluated using the syntax of arguments[index] and has the length attribute. The arguments object stores the parameters actually passed to the function, and is not limited to the parameter list defined by the function declaration. For example:

Js code

function func(a,b){  
    alert(a);  
    alert(b);  
    for(var i=0;i<arguments.length;i++){  
        alert(arguments[i]);  
    }  
}  
func(1,2,3,4);

When the code is run, it will be displayed in sequence: 1, 2, 1, 2, 3 ,4. The function defines two parameters, but 4 parameters are passed when called.

2. The callee attribute of arguments
It represents a reference to the function object itself, which is beneficial to realizing the recursion of the unnamed function or ensuring the encapsulation of the function. For example: Use recursion to calculate the sum of natural numbers from 1 to n:

Js code

var sum=function(n){  
    if(1==n) {  
        return 1;  
    } else {  
        return n + arguments.callee(n-1);  
    }  
}  
alert(sum(100));

arguments.callee represents a reference to the currently executing function, or a reference to the function object that calls arguments.callee, which gives the anonymous function Provides a way to self-reference.

More in-depth, including caller, call, apply

Js code

/* 
 * 演示arguments的用法,如何获取实参数和形数数 
 */  
function argTest(a,b,c,d){  
    var numargs = arguments.length;     // 获取被传递参数的数值。  
    var expargs = argTest.length;       // 获取期望参数的数值。  
    alert("实参数目为:"+numargs)  
    alert("形数数目为:"+expargs)  
  
    alert(arguments[0])           
    alert(argTest[0])          //undefined 没有这种用法  
}  
//argTest(1,2)  
//argTest(1,2,3,4,5)  
  
  
/* 
 *  arguments不是数组(Array类) 
 */  
  
Array.prototype.selfvalue = 1;  
function testAguments(){  
    alert("arguments.selfvalue="+arguments.selfvalue);  
}  
//alert("Array.sefvalue="+new Array().selfvalue); // 1  
//testAguments();  //arguments.selfvalue = undefined  
  
  
  
/* 
 * 演示函数的callee属性. 
 * 说明:arguments.callee:初始值就是正被执行的 Function 对象,用于匿名函数 
 */  
function calleeDemo() {  
    alert(arguments.callee);  
}  
//calleeDemo();  
//(function(arg0,arg1){alert("形数数目为:"+arguments.callee.length)})();  
  
  
  
  
/* 
 * 演示函数的caller属性. 
 * 说明:(当前函数).caller:返回一个对函数的引用，该函数调用了当前函数 
 */  
  
function callerDemo() {  
    if (callerDemo.caller) {  
        var a= callerDemo.caller.arguments[0];  
        alert(a);  
    } else {  
        alert("this is a top function");  
    }  
}  
function handleCaller() {  
    callerDemo();  
}  
  
//callerDemo();  
//handleCaller("参数1","参数2");  
  
  
  
  
  
/* 
 * 演示apply,call函数的用法 
 * 说明:作用都是将函数绑定到另外一个对象上去运行，两者仅在定义参数方式有所区别： 
 *       apply(thisArg,argArray); 
 *     call(thisArg[,arg1,arg2…] ]); 
 *     即所有函数内部的this指针都会被赋值为thisArg 
 */  
  
 function ObjectA(){  
    alert("执行ObjectA()");  
    alert(arguments[0]);  
    alert(this.b);//在ObjectB中用call/apply调用ObjectA时，ObjectB的变量b的值。  
    this.hit=function(msg){alert(msg)}  
    this.info="我来自ObjectA"  
 }  
   
 function ObjectB(){  
    alert("执行ObjectB()");  
    this.b = '2b';  
    //调用ObjectA()方法,同时ObjectA构造函数中的所有this就会被ObjectB中的this替代  
    ObjectA.apply(this,arguments);//ObjectA.call(this);  
    alert(this.info);  
 }  
 //ObjectB('参数0');  
  
  
 var value="global 变量";  
 function Obj(){  
    this.value="对象！";  
 }  
 function Fun1(){  
    alert(this.value);  
 }  
 //Fun1();  
 //Fun1.apply(window);   
 //Fun1.apply(new Obj());