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javascriptmathroundingnumber-formatting

Rounding Issue with Javascript using Math


I'm working on a project where I have an input field where a user puts in a dollar amount and depending on the frequency they would like to pay it divides that amount by said value (2, 4, or 12). So for instance if I put in an amount of $5 and had the frequency set at 2, I would have it display $2.50 for the charge amount. The issue I am having is if a user inputs $20.27 with frequency set at 2, I would expect to see $10.14 as the display but for some reason am getting $10.13 even after using Math.round and a toFixed(2). If I input $2.27 or $0.27 I do get the expected $1.14 and $.14 respectively but as soon as I get to more than $10 it no longer rounds correctly. I cannot figure out what I am doing wrong. Here is my code:

const setAmount = (num) => {
        scope.selectAmount(selectedAmount / num);
        finalAmount = ((Math.round(selectedAmount * 100) / 100) / num).toFixed(2);
        selectedAmountText = '$' + finalAmount;
        $('#pay-schedule span').text(selectedAmountText);

    }

Any help would be tremendously appreciated. Thanks!


Solution

  • I don't have an exact explanation for this but dividing by 2 at the end makes it somewhat inconsistent. So diving the number by 2 in the first place solves the issue for the specific values that you've provided.

    function round(num) {
      let val = num / 2
      return (Math.round(val * 100) / 100).toFixed(2);
    }