javascript自动生成包含数字与字符的随机字符串

　　*

　　*    随机生成数字

　　*

　　*@param num 生成数字位数

　　*/

　　function randomNumber(num){

　　return ''+Math.floor(Math.random() * num) ;

　　}

　　*

　　*    随机生成

　　*

　　*@param data json数据 例：{"start":0,"end":2,"number":5,"upper":true}

　　*@param start  开始下标

　　*@param end    结束下标

　　*@param number 生成位数

　　*@param upper  是否大写 默认为小写

　　*/

　　function randomLetter(data){

　　var letterData = "";

　　var lowercase = new Array("a","b","c","d","e","f","g","h","i","g","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z");

　　var uppercase = new Array("A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z");

　　var start = data.start;

　　var end = data.end;

　　var number = data.number;

　　var upper = data.upper;

　　var length = end - start;

　　for(var i= 0;i < number; i++){

　　var index = Math.floor(Math.random() * length) + start;

　　var letter = "";

　　if(upper){

　　letter = uppercase[index];

　　}else{

　　letter = lowercase[index];

　　}

　　letterData += letter;

　　}

　　return letterData;

　　}