function outer(){
 var val = 0;
 return function (){
  val += 1;
  document.write(val + "<br />");
 };
}
var outObj = outer();
outObj();//1，执行val += 1后，val还在
outObj();//2
outObj = null;//val 被回收
var outObj1 = outer();
outObj1();//1
outObj1();//2

function doSomething(callback){
 callback(1,2);
}
function numberAdd(a,b){
 document.write(a+b);
}
doSomething(numberAdd);//3

function Thing(name){
 this.name = name;
}

Thing.prototype.doSomething = function(callback){
 callback(this.name);
};
function showName(name){
 document.write(name);
}
var t = new Thing("zhangsan");
t.doSomething(showName);//zhangsan

var arr = [25,13,33,8,23,32];
Array.prototype.sort = function(callback){
 var arr = this;
 var i = 0;//i在这里定义与在for循环的括号内（for(var i = 0; i < ...)）定义是一样的
 for(; i < arr.length-1; i++){
  var j = i + 1;
  for(; j < arr.length;j++){
  if(callback(arr[i],arr[j])){
   var temp = arr[i];
   arr[i] = arr[j];
   arr[j] = temp;
  }
  } 
 }
return arr;
};
//a-b>0表示数组从小到大排序
arr.sort(function(a,b){
 return a - b > 0;
});
document.write(arr.join(",") + "<br />");//8,13,23,25,32,33
//b-a>0表示数组从大到小排序
arr.sort(function(a,b){
 return b - a > 0;
});
document.write(arr.join(","));//33,32,25,23,13,8