<script>
    $(function(){
        $('#number0').blur(function(){
            num = $('#number0').val();
            if(!isNaN(num)){
                scale = $('#scale0').val();
                $('#cny0').val(accMul(num,scale));
            }
        });
    });
    function accMul(arg1,arg2)
    {
        var m=0,s1=arg1.toString(),s2=arg2.toString();
        try{m+=s1.split(".")[1].length}catch(e){}
        try{m+=s2.split(".")[1].length}catch(e){}
        return Number(s1.replace(".",""))*Number(s2.replace(".",""))/Math.pow(10,m)
    }
</script>

<script>
function badFloat(num, size){
    if(isNaN(num)) return true;
    num += '';
    if(-1 == num.indexOf('.')) return false;
    var f_arr = num.split('.');
    if(f_arr[1].length > size){
        return true;
    }
    return false;
}
// 格式化小数
//@f float 传入小数: 123; 1.1234; 1.000001;
//@size int 保留位数
//@add bool 进位: 0 舍 1 进
function formatfloat(f, size, add){
  f = parseFloat(f);
  if(size == 2) conf = [100,0.01];
  if(size == 3) conf = [1000,0.001];
  if(size == 4) conf = [10000,0.0001];
  if(size == 5) conf = [100000,0.00001];
  if(size == 6) conf = [1000000,0.000001];
  if(size == 7) conf = [10000000,0.0000001];
    if(size == 8) conf = [100000000,0.00000001];
  var ff = Math.floor(f * conf[0]) / conf[0];
  if(add && f > ff) ff += conf[1];
  return isNaN(ff)? 0: ff;
}
function vNum(o, len){
    if($("#buy_price").val()!="" && $("#buy_num").val()!=""){
        if(badFloat(o.value, len))
        o.value=formatfloat(o.value,len,0);
        var ci = $("#buy_price").val()*$("#buy_num").val();
        $("#buy_money").text(Math.round(ci*100)/100);
    }
}
</script>

onkeyup="vNum(this,2);"
TODO：第二种 Jquery 的小数点验证可以替换为，
<form action="/example/html5/demo_form.asp" method="get">
Points: <input type="number" name="points" min="2" step="0.01" />
<input type="submit" />
</form>