js对浮点数进行四舍五入，按需要保留小数位数

function formatNumber(pnumber,decimals){

 if (isNaN(pnumber) || pnumber=='') { return 0};

 

 var snum = new String(pnumber);

 var sec = snum.split('.');

 var whole = parseFloat(sec[0]);

 var result = '';

 

 if (sec.length > 1){

  var dec = new String(sec[1]);

  dec = String(parseFloat(sec[1])/Math.pow(10,(dec.length - decimals)));

  dec = String(whole + Math.round(parseFloat(dec))/Math.pow(10,decimals));

  var dot = dec.indexOf('.');

  if (dot == -1){

   dec += '.';

   dot = dec.indexOf('.');

  }

  while(dec.length <= dot + decimals) { dec += '0'; }

  result = dec;

 } else{

  var dot;

  var dec = new String(whole);

  dec += '.';

  dot = dec.indexOf('.');   

  while(dec.length <= dot + decimals) { dec += '0'; }

  result = dec;

 } 

 return result;

}