方法一
var character = new Array("A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","X","Y","Z");
for(var i=0;i<25;i++)
{
alert(character[i]);
}
方法二
for(var i=0;i<25;i++)
{
alert(String.fromCharCode((65+i)));
}
附带：js大小写转换
strVariable.toUpperCase( ) 转大写
stringVar.toLowerCase( ) 转小写