Math equations with javascript not working correctly

Question

I was writing a formula in javascript to help me easily calculate the break even formula when trading stocks. The formula is to calculate the break even point is: ((shares x price)+commission)/(shares)

So for my code I wrote:

<script type="text/javascript" language="javascript" charset="utf-8">

function output(){
var value1 = document.getElementById('value1').value;
var value2 = document.getElementById('value2').value;
var value3 = document.getElementById('value3').value; 
document.getElementById('result').innerHTML = ((parseInt(value1) * parseInt(value2)) +      (parseInt(value3))) / (parseInt(value2));
}

</script>

However, when I run it I don't get the correct answer. For example, when shares = 20, price = 8.88 and commission = 10, it gives me the answer as 8.5, but the correct answer is 9.38.

Can anyone tell me where I went wrong, thanks.

Answer 1

You are calling parseInt instead of parseFloat, so you are losing the fractional parts for your numbers.

document.getElementById('result').innerHTML = ((parseFloat(value1) * parseFloat(value2)) +      (parseFloat(value3))) / (parseFloat(value2));

A slightly terser way of doing it is to use the unary plus operator when you get each value:

var value1 = +document.getElementById('value1').value;
var value2 = +document.getElementById('value2').value;
var value3 = +document.getElementById('value3').value; 
document.getElementById('result').innerHTML = ((value1 * value2) + value3) / value2;

Answer 2

That's because the price is being parsed as an integer. Integers can't have decimals, so it's rounded down to 8.

Use parseFloat instead of parseInt for the price.

Answer 3

使用parseFloat代替parseInt ，当使用parseInt您最终将获得(20 * 8 + 10) / 20 ，而不是(20 * 8.88 + 10) / 20 。