Convert Fraction String to Decimal?

Question

I'm trying to create a javascript function that can take a fraction input string such as '3/2' and convert it to decimal—either as a string '1.5' or number 1.5

function ratio(fraction) {
    var fraction = (fraction !== undefined) ? fraction : '1/1',
    decimal = ??????????;
    return decimal;
});

Is there a way to do this?

Answer 1

If you don't mind using an external library, math.js offers some useful functions to convert fractions to decimals as well as perform fractional number arithmetic.

console.log(math.number(math.fraction("1/3"))); //returns 0.3333333333333333
console.log(math.fraction("1/3") * 9) //returns 3

<script src="https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.20.1/math.js"></script>

Answer 2

It works with eval() method but you can use parseFloat method. I think it is better! Unfortunately it will work only with that kind of values - "12.2" not with "5/8", but since you can handle with calculation I think this is good approach!

Answer 3

Too late, but can be helpful:

You can use Array.prototype.reduce instead of eval https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

ES6

const fractionStrToDecimal = str => str.split('/').reduce((p, c) => p / c);
console.log(fractionStrToDecimal('1/4/2')); // Logs 0.125
console.log(fractionStrToDecimal('3/2')); // Logs 1.5

CJS

function fractionStrToDecimal(str) {
  return str.split('/').reduce((p, c) => p / c);
}
console.log(fractionStrToDecimal('1/4')); // Logs 0.25

[EDIT] Removed reducer initial value and now the function works for numerators greater than 1. Thanks, James Furey.

Answer 4

Also a bit late to the party, but an alternative to eval() with less security issues (according to MDN at least) is the Function() factory.

var fraction = "3/2";
console.log( Function("return (" + fraction + ");")() );

This would output the result "1.5" in the console.

Also as a side note: Mixed fractions like 1 1/2 will not work with neither eval() nor the solution with Function() as written as they both stumble on the space.

Answer 5

To convert a fraction to a decimal, just divide the top number by the bottom number. 5 divided by 3 would be 5/3 or 1.67. Much like:

function decimal(top,bottom) {
    return (top/bottom)
}

Hope this helps, haha

Answer 6

I have a function I use to handle integers, mixed fractions (including unicode vulgar fraction characters), and decimals. Probably needs some polishing but it works for my purpose (recipe ingredient list parsing).

• NPM
• GitHub

Inputs "2 1/2", "2½", "2 ½", and "2.5" will all return 2.5. Examples:

var numQty = require("numeric-quantity");

numQty("1 1/4") === 1.25;  // true
numQty("3 / 4") === 0.75;  // true
numQty("¼" ) === 0.25;     // true
numQty("2½") === 2.5;      // true
numQty("¾") === 0.75;      // true
numQty("⅓") === 0.333;     // true
numQty("⅔") === 0.667;     // true

One thing it doesn't handle is decimals within the fraction, e.g. "2.5 / 5".