js实现数字每三位加逗号的方法

js实现数字每三位加逗号的方法，摘自：http://www.jb51.net/article/60801.htm

function formatNum(str){
  var newStr = "";
  var count = 0;

  if(str.indexOf(".")==-1){
    for(var i=str.length-1;i>=0;i--){
      if(count % 3 == 0 && count != 0){
        newStr = str.charAt(i) + "," + newStr;
      }else{
        newStr = str.charAt(i) + newStr;
      }
      count++;
    }
    str = newStr + ".00"; //自动补小数点后两位
  }
  else
  {
    for(var i = str.indexOf(".")-1;i>=0;i--){
      if(count % 3 == 0 && count != 0){
        newStr = str.charAt(i) + "," + newStr;
      }else{
        newStr = str.charAt(i) + newStr; //逐个字符相接起来
      }
      count++;
    }
    str = newStr + (str + "00").substr((str + "00").indexOf("."),3);
  }
  return str;
}

formatNum('13213.24'); //输出13,213.24

formatNum('132134.2');  //输出132,134.20

formatNum('132134');  //输出132,134.00

formatNum('132134.236');  //输出132,134.23