Javascript loop

1. for
   

   var myArray = [1,2,3];
   for (var i = 0; i < myArray.length; i++) 
   {
       alert(myArray[i]);
   }
   

   output
   --------------------------------------------
   1
   2
   3
   
   
2. for in
   

   var obj = 
   {
       a : 1,
       b : 2
   };
   
   for(var key in obj) 
   {
      alert(key);
   }
   

   output
   --------------------------------------------
   a
   b
   
   
3. forEach (IE9 之後才支援)
   forEach 是從 Array.prototype.forEach 來的, 因此只要是 Array 物件就擁有 forEach 方法
   

   function alertElements(element, index, array) 
   {
       alert(element);
   }
   [1,2,3].forEach(alertElements);
   

   output
   --------------------------------------------
   1
   2
   3
   
   在 ECMAScript 5, 也可使用 forEach 取得物件屬性名稱
   

   var obj = 
   {
       a : 1,
       b : 2
   };
   
   Object.keys(obj).forEach(function(key) 
   {
       alert(key);
   });
   

   output
   --------------------------------------------
   a
   b
   
   
4. while
   

   var i=0;
   var myArray = [1,2,3];
   
   while(myArray[i])
   {
       alert(myArray[i]);
       i++;
   }
   

   output
   --------------------------------------------
   1
   2
   3
   
   
5. do while
   

   var i = 1;
   var sum = 0;
        
   do 
   {
       sum += i;
       i++;
   } 
   while (i <= 100);
   
   alert(sum);
   

   output
   --------------------------------------------
   5050