javascript - JS - Numbers rounded in real time -

i created form enable users have quote:

    <form name="autosumform"> <br><br> width: <input class="right" type="text" name="firstbox" value="" onblur="stopcalc();"><br> height: <input class="right" type="text" name="secondbox" value="" onblur="stopcalc();"><br> type: <select class="right" name="thirdbox" onfocus="startcalc();" onblur="stopcalc();">         <option selected="selected">-</option>         <option value="7.80">forex bianco 3 mm</option>         <option value="8.30">forex bianco 5 mm</option>         <option value="9.90">forex bianco 10 mm</option>         <option value="5.70">forex piuma 10 mm</option>     </select><br> total cost: <input class="right" type="text" name="fourbox"> </form> 

i wrote little js calculate total cost:

function startcalc(){   interval = setinterval("calc()",1); } function calc(){   1 = document.autosumform.firstbox.value;   2 = document.autosumform.secondbox.value;   3 = document.autosumform.thirdbox.value;   document.autosumform.fourbox.value = (one * 1) * (two * 1) * (0.0001) * (three * 1); } function stopcalc(){   clearinterval(interval); } function roundnumber(number, decimals){     var newnumber = new number(fourbox).tofixed(parseint(decimals));     document.autosumform.fourbox.value =  parsefloat(newnumber); } 

now problem is: every time fill form result number many digits after comma, tryed many things no 1 went good... please help! thank you!!!

ps know better server side type of work, it's simple site , every order processed person.

ok, i'm not 100% sure trying calculate here changes think may trying achieve, if not may @ least set in right direction. btw, better use "id" rather "name" identifying elements "id" must unique.

html

<form name="autosumform">     <br>     <br>width:     <input class="right" type="text" name="firstbox" value="">     <br>height:     <input class="right" type="text" name="secondbox" value="">     <br>type:     <select class="right" name="thirdbox">         <option selected="selected">-</option>         <option value="7.80">forex bianco 3 mm</option>         <option value="8.30">forex bianco 5 mm</option>         <option value="9.90">forex bianco 10 mm</option>         <option value="5.70">forex piuma 10 mm</option>     </select>     <br>total cost:     <input class="right" type="text" name="fourbox" value="0.00"> </form> 

javascript

var firstbox = document.queryselector("[name='firstbox']"); var secondbox = document.queryselector("[name='secondbox']"); var thirdbox = document.queryselector("[name='thirdbox']"); var fourbox = document.queryselector("[name='fourbox']");  function update() {     fourbox.value = ((parsefloat(firstbox.value) * parsefloat(secondbox.value) * 0.0001 * parsefloat(thirdbox.value)) || 0).tofixed(2); }  firstbox.addeventlistener("keyup", update, false); secondbox.addeventlistener("keyup", update, false); thirdbox.addeventlistener("change", update, false); 

on jsfiddle

wrt comment parsefloat vs unary plus operator

it possible unary plus operator faster in case (when?), on 2 of popular browsers (chrome , firefox), jsperf shows parsefloat faster

i think parsefloat shows intent far clearer pre-pending "+", shorter code not better code

there differences between 2 methods when converting string, consider jsfiddle