js中arguments对象的深入理解

function f1(){
  console.log(arguments[0]);
  console.log(arguments[1]);
  console.log(arguments[2]);
 }

 f1(12,23,45); //12 34 45

function f2(a,b){
  arguments[0] = 10;
  arguments[1] = 20;
  return a + b;
 }

 console.log(f2(4,6)); //30

function f3(a,b){
  'use strict';
  arguments[0] = 10;
  arguments[1] = 20;
  return a + b;
 }

 console.log(f3(3,6)); //9

 function f4(){
  console.log(arguments.length);
 }

 f4(2,3,4,5); //4
 f4(1);  //1
 f4();  //0

var arr = Array.prototype.slice.call(arguments);
  console.log(typeof arr);

  var arr2 = [];
  for(var i = 0; i<arguments.length;i++){
   arr2.push(arguments[i]);
  }
  console.log(typeof arr2);

var f5 = function(){
   console.log(arguments.callee===f5); //true
   console.log(arguments.callee===f6); //false
  }
  
  var f6;
  f5(); //返回原函数，调用自身

function add(a, b) { 

 var realLen = arguments.length; 
 console.log("realLen:", arguments.length); 
 var len = add.length; 
 console.log("len:", add.length); 

 if (realLen == len) { 
 console.log('实参和形参个数一致'); 
 } else { 
 console.log('实参和形参个数不一致'); 
 } 

}; 

add(11,22,33,44,66);

var sum = function(n) { 

 if(n == 1) { 
  return 1; 
 } else { 
  return n + arguments.callee(n-1); 
　 } 
 } 

console.log("sum =", sum(5)); 

function add() { 

var len = arguments.length; 
var sum = 0; 

for (var i = 0; i < len; ++i) { 
  sum += arguments[i]; 
} 
return sum; 
}; 

add(11,22,33,44,66);