javascript生成随机大小写字母的方法

/** 
* 返回一个随机的小写字母 
*/ 
function getLowerCharacter(){ 
return getCharacter("lower");; 
} 
/** 
* 返回一个随机的大写字母 
*/ 
function getUpperCharacter(){ 
return getCharacter("upper");; 
} 

/** 
* 返回一个字母 
*/ 
function getCharacter(flag){ 
var character = ""; 
if(flag === "lower"){ 
character = String.fromCharCode(Math.floor( Math.random() * 26) + "a".charCodeAt(0)); 
} 
if(flag === "upper"){ 
character = String.fromCharCode(Math.floor( Math.random() * 26) + "A".charCodeAt(0)); 
} 
return character; 
}