前端工具函数，持续更新...

// 每隔三位加逗号
function formatNum(str){
  var str = ''+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
      str = newStr;
  }
  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;
}

来源：CSDN

作者：dreamStart_Lin

链接：https://blog.csdn.net/dreamStart_Lin/article/details/104178553