JavaScript math, round to two decimal places [dupl

Question

This question already has an answer here:

• Round to at most 2 decimal places (only if necessary) 59 answers

I have the following JavaScript syntax:

var discount = Math.round(100 - (price / listprice) * 100);

This rounds up to the whole number. How can I return the result with two decimal places?

Answer 1

To get the result with two decimals, you can do like this :

var discount = Math.round((100 - (price / listprice) * 100) * 100) / 100;

The value to be rounded is multiplied by 100 to keep the first two digits, then we divide by 100 to get the actual result.

Answer 2

The functions Math.round() and .toFixed() is meant to round to the nearest integer. You'll get incorrect results when dealing with decimals and using the "multiply and divide" method for Math.round() or parameter for .toFixed(). For example, if you try to round 1.005 using Math.round(1.005 * 100) / 100 then you'll get the result of 1, and 1.00 using .toFixed(2) instead of getting the correct answer of 1.01.

You can use following to solve this issue:

Number(Math.round(100 - (price / listprice) * 100 + 'e2') + 'e-2');

Add .toFixed(2) to get the two decimal places you wanted.

Number(Math.round(100 - (price / listprice) * 100 + 'e2') + 'e-2').toFixed(2);

You could make a function that will handle the rounding for you:

function round(value, decimals) {
    return Number(Math.round(value + 'e' + decimals) + 'e-' + decimals);
}

Example: https://jsfiddle.net/k5tpq3pd/36/

Alternativ

You can add a round function to Number using prototype. I would not suggest adding .toFixed() here as it would return a string instead of number.

Number.prototype.round = function(decimals) {
    return Number((Math.round(this + "e" + decimals)  + "e-" + decimals));
}

and use it like this:

var numberToRound = 100 - (price / listprice) * 100;
numberToRound.round(2);
numberToRound.round(2).toFixed(2); //Converts it to string with two decimals

Example https://jsfiddle.net/k5tpq3pd/35/

Source: http://www.jacklmoore.com/notes/rounding-in-javascript/

Answer 3

function discoverOriginalPrice(discountedPrice, salePercentage) {
  var originalPrice = discountedPrice / (1 - (salePercentage * .01));
  return +originalPrice.toFixed(2);
}

Answer 4

To handle rounding to any number of decimal places, a function with 2 lines of code will suffice for most needs. Here's some sample code to play with.

    var testNum = 134.9567654;
    var decPl = 2;
    var testRes = roundDec(testNum,decPl);  
    alert (testNum + ' rounded to ' + decPl + ' decimal places is ' + testRes);

    function roundDec(nbr,dec_places){
        var mult = Math.pow(10,dec_places);
        return Math.round(nbr * mult) / mult;
    }

Answer 5

    function round(num,dec)
    {
      num = Math.round(num+'e'+dec)
      return Number(num+'e-'+dec)
    }
      //Round to a decimal of your choosing:
    round(1.3453,2)

Answer 6

The best and simple solution I found is

function round(value, decimals) {
  return Number(Math.round(value+'e'+decimals)+'e-'+decimals);
}

round(1.005, 2); // 1.01

Reference: http://www.jacklmoore.com/notes/rounding-in-javascript/