我们已见到了很多所请求的X`S，现在复习一下：

第一步：请求X`S的数目

var width = prompt("How many x's would you like? (1-10 is good)","5");

var a_line="";

var loop = 0;

while (loop < width)

{

	a_line = a_line + "x";

	loop=loop+1;

}

即说：“当变量循环小于所请求的X`S行宽时，在该行加入另一X然后在循环值上加1。”该循环将继续加一X到该行并在循环值上加1直到循环不在小于请求的行宽。请看下列源码分析：

第一次

• a_line = "" (because we initialized it to be "")

• loop=0 (because we initialized it to be 0)

• width=2 (because that's what the user asked for)

• 0 is less than 2 so

• a_line = a_line + "x", so now a_line = "x"

• loop=loop+1, so now loop = 1

返回循环：第二次

• loop=1

• width=2

• a_line = "x"

• 1 is less than 2 so

• a_line = a_line + "x", so now a_line = "xx"

• loop=loop+1, so now loop = 2

返回循环：第3次

• loop=2

• width=2

• a_line = "xx"

• 2 is NOT less than 2 so

• fall out of the loop and do what follows

alert(a_line);

while (loop < width)

{

	a_line += "x";  //this was a_line = a_line + "x";

	loop++;         //this was loop=loop+1;

}

首行，“x”，表示“本身加x”。若已有a_number=5，那么可写成，a_number+=3，即是说：a_number=a_number+3。程序员就是这么偷懒的。

下行，loop++，意味着“自身加1”。于是loop++即为：loop=loop=1。它也可写成loop+=1。这样偷懒行为非常有效。

就象不止一种方式在一个数上加1一样，也有不止一种方法来写一个循环。While循环不是唯一的循环模式，另一流行的循环是forloop