parseFloat rounding

I have javascript function that automatically adds input fields together, but adding numbers like 1.35 + 1.35 + 1.35 gives me an output of 4.050000000000001, just as an example. How can I round the total to the second decimal instead of that long string?

The input fields will have more than just the 1.35 example so I need the total to never have more than 2 points after the decimal. Here is the full working code:

<html>
<head>
<script type="text/javascript">
function Calc(className){
var elements = document.getElementsByClassName(className);
var total = 0;

for(var i = 0; i < elements.length; ++i){
total += parseFloat(elements[i].value);
}

document.form0.total.value = total;
}

function addone(field) {
  field.value = Number(field.value) + 1;
  Calc('add');
}
</script>
</head>
<body>
<form name="form0" id="form0">
1: <input type="text" name="box1" id="box1" class="add" value="0" onKeyUp="Calc('add')" onChange="updatesum()" onClick="this.focus();this.select();" />
<input type="button" value=" + " onclick="addone(box1);">
<br />

2: <input type="text" name="box2" id="box2" class="add" value="0" onKeyUp="Calc('add')" onClick="this.focus();this.select();" />
<input type="button" value=" + " onclick="addone(box2);">
<br />

<br />
Total: <input readonly style="border:0px; font-size:14; color:red;" id="total" name="total">
<br />
</form>
</body></html>

Some things I have tried, which should work but I am clearly implementing them incorrectly:

for(var i = 0; i < elements.length; ++i){
total += parseFloat(elements[i].value.toString().match(/^\d+(?:\.\d{0,2})?/));

var str = total.toFixed(2);

for(var i = 0; i < elements.length; ++i){
total += parseFloat(elements[i].value * 100) / 100).toFixed(2)

Have also had no luck with Math.floor

标签： javascript math parsefloat

5条回答

我想做一个坏孩纸

2楼-- · 2019-01-11 12:41

This works:

$(document).ready(
    function() {
            $('#field1').blur(function(){ $('#field2').val(parseFloat($(this).val() * 2.2).toFixed(1)); });
            $('#field2').blur(function(){ $('#field1').val(parseFloat($(this).val() / 2.2).toFixed(1)); });
    }
);

This fails:

$(document).ready(
    function() {
            $('#field1').blur(function(){ $('#field2').val(parseFloat($(this).val() * 2.2)).toFixed(1); });
            $('#field2').blur(function(){ $('#field1').val(parseFloat($(this).val() / 2.2)).toFixed(1); });
    }
);

So be careful the way you place your parenthesis ()... In first case, the rounding will work, but won't work in the second one...

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Animai°情兽

3楼-- · 2019-01-11 12:50

You can use Math.round(total*100000000000)/100000000000; in the code. It will work for most of the cases

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你好瞎i

4楼-- · 2019-01-11 12:56

Use toFixed() to round num to 2 decimal digits using the traditional rounding method. It will round 4.050000000000001 to 4.05.

num.toFixed(2);

You might prefer using toPrecision(), which will strip any resulting trailing zeros.

Example:

1.35+1.35+1.35 => 4.050000000000001
(1.35+1.35+1.35).toFixed(2)     => 4.05
(1.35+1.35+1.35).toPrecision(3) => 4.05

// or...
(1.35+1.35+1.35).toFixed(4)     => 4.0500
(1.35+1.35+1.35).toPrecision(4) => 4.05

Reference: JavaScript Number Format - Decimal Precision

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淡お忘

5楼-- · 2019-01-11 13:00

Instead of rounding, you may want to use the port of Java's BigDecimal to get actually precise decimal math.

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The star\"

6楼-- · 2019-01-11 13:07

var num = 4.050000000000001;

num = num.toFixed(2);

toFixed will round up depending on how many digits after the decimal you're looking for.

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parseFloat rounding

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