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\'

Answer 1

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 2

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".

Answer 3

safer eval() according to MDN

const safeEval = (str) => {
   return Function('"use strict";return (' + str + ")")();
}

safeEval("1 1/2") // 1.5

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#Do_not_ever_use_eval!

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 created a nice function to do just that, everything was based off of this question and answers but it will take the string and output the decimal value but will also output whole numbers as well with out errors

https://gist.github.com/drifterz28/6971440

function toDeci(fraction) {
    fraction = fraction.toString();
    var result,wholeNum=0, frac, deci=0;
    if(fraction.search('/') >=0){
        if(fraction.search('-') >=0){
            wholeNum = fraction.split('-');
            frac = wholeNum[1];
            wholeNum = parseInt(wholeNum,10);
        }else{
            frac = fraction;
        }
        if(fraction.search('/') >=0){
            frac =  frac.split('/');
            deci = parseInt(frac[0], 10) / parseInt(frac[1], 10);
        }
        result = wholeNum+deci;
    }else{
        result = fraction
    }
    return result;
}

/* Testing values / examples */
console.log('1 ',toDeci("1-7/16"));
console.log('2 ',toDeci("5/8"));
console.log('3 ',toDeci("3-3/16"));
console.log('4 ',toDeci("12"));
console.log('5 ',toDeci("12.2"));