Decimal to Fraction in JavaScript

Question

I wrote this simple script to convert a decimal to a fraction but it is not working. Nothing is outputted.

var decimal = 1.75;
var decimalArray = decimal.split("."); // 1.75
var leftDecimalPart = decimalArray[0]; // 1
var rightDecimalPart = decimalArray[1]; // 75

var numerator = leftDecimalPart + rightDecimalPart; // 175
var denominator = Math.pow(10, rightDecimalPart.length); // 100

document.write(numerator + " / " + denominator);

JS Bin: http://jsbin.com/exepir/1/edit

You have wrong output. `numerator/denominator` will give the fraction, not vice versa. — VisioN, Jan 24 '13 at 21:25
@bfavaretto for 0.2 it returns `02 / 10` which is correct. Nothing suggests it would be a reduced fraction. — sachleen, Jan 24 '13 at 21:25
I failed to see the whole picture, VisioN is right. On your current code numerator and denominator are inverted. — bfavaretto, Jan 24 '13 at 21:26
@user1822824 see [Is there a javascript function that reduces a fraction](http://stackoverflow.com/questions/4652468/is-there-a-javascript-function-that-reduces-a-fraction) for how to reduce fractions if you want to implement that. — sachleen, Jan 24 '13 at 21:27
I don't want to reduce. I have a separate function for that. — user1822824, Jan 24 '13 at 21:29

sachleen · Accepted Answer · 2013-01-24T21:29:53.617

You can't "split" numbers.

If you look at the console, you'll see

Uncaught TypeError: Object 1.75 has no method 'split'

You should be using the JavaScript section on JSBin, it'll show you errors like this in a red box at the bottom.

Easiest fix? Make it a string by either writing it as a string literal:

var decimal = '1.75';

Or call .toString() before splitting:

var decimalArray = decimal.toString().split(".");

And numerator is on top:

document.write(numerator + " / " + denominator);

score 2 · Answer 2 · answered Jan 24 '13 at 21:53

Since working with strings is not the best way to solve your problem, I'd suggest you a fast alternative solution which works with numbers only:

var decimal = 1.75,
    numerator = decimal,
    denominator = 1;

while (numerator % 1) numerator *= 10;
denominator = numerator / decimal;

console.log(numerator + " / " + denominator);
// >> "175 / 100"

score 2 · Answer 3 · answered Jun 04 '15 at 12:17

If you want to make sure it works in the general case, I would rely on a well tested library, like Fraction.js.

var f = new Fraction(1.75);

console.log(f.toFraction()); // Results "1 3/4"
console.log(f.s * f.n + " / " + f.d); // Results "7 / 4"
console.log(f.toString()); // Results "1.75"

Decimal to Fraction in JavaScript

3 Answers3

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