How to sum values from a checkbox using javascript

StackOverflow https://stackoverflow.com/questions/20672741

  •  19-09-2022
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题

Hey all I am trying to update this code I have. It pretty much does what I need it to except one thing. Well two technically, but mostly one I am concerned with. When I check off the boxes I want, it adds up like it is supposed to and adds 5% on top like its supposed to, however it puts the answer in the value of my submit button. How can I stop this from happening? Second (and less important for now) How can I make that total value return as a dollar amount with only 2 decimal points, so instead of returning 0.924 it returns $.92 for example. Thanks!

<body>
<h1> The Fruit Form</h1>
<form action="" name="form1" id="form1">
<input type="checkbox" id='fruit0' value=".59" >Apples ( .59)<br>
<input type="checkbox" id='fruit1' value=".49">Oranges (.49)<br>
<input type="checkbox" id='fruit2' value=".39">Bananas(.39)<br>

<input type="submit" onclick="UpdateCost()" id="totalcost" value="Submit">

</form>
<script type="text/javascript">
function UpdateCost() {
  var sum = 0;
  var fid, elem;
  for (i=0; i<3; i++) {
    fid = 'fruit'+i;
    elem = document.getElementById(fid);
    if (elem.checked == true) { sum += Number(elem.value); }
  }
  document.getElementById('totalcost').value = sum.toFixed(2)*1.05;
  alert("Your Total Is:" + totalcost.value);
  return false
} 
</script>
</body>
有帮助吗？

解决方案

Your submit-button's id is totalcost and your function gets the element with the id totalcost:

document.getElementById('totalcost').value = sum.toFixed(2)*1.05;

So you can prevent this by not doing this.

Instead of sum.toFixed(2)*1.05 you should do (sum * 1.05).toFixed(2) as was commented by PSL.

Instead, update your variable:

sum = (sum * 1.05).toFixed(2);

or create a new variable say total:

var total = (sum * 1.05).toFixed(2);

or just process it where you output the value:

alert(  (sum * 1.05).toFixed(2)  );

Extra:
Since you are working with money up to 2 decimal points, I'd like to make you aware of the fact that in javascript 0.1+0.2 is NOT 0.3!

The best way to avoid that is to multiply all numbers by the accuracy you need and devide the final (sub-) result by that precision on output.

So: (52 cents + 18 cents = 70 cents) / 100 = 0.7 (and here you'd use toFixed so it becomes 0.70 ).

其他提示

Just some code comments:

If can get a reference to the form if you pass this to the function:

<input type="submit" onclick="UpdateCost(this)"  ...>

In the function:

function UpdateCost(element) {
  var sum = 0;
  var fid, elem;

Store a reference to the form:

  var form = element.form;

  for (i=0; i<3; i++) {
    fid = 'fruit'+i;
    elem = document.getElementById(fid);

The above can be:

    elem = form[fid];

    if (elem.checked == true) {
      sum += Number(elem.value);
    }

And that can be:

    sum += elem.checked? +elem.value : 0;

where the unary + will convert the value to a number.

  }
  document.getElementById('totalcost').value = sum.toFixed(2)*1.05;

becomes:

  form.totalcost.value = '$' + (sum * 1.05).toFixed(2);

HTH.

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