Convert a decimal number to a fraction / rational number

Question

In JavaScript, is there any way to convert a decimal number (such as 0.0002) to a fraction represented as a string (such as \"2/10000\")?

I

Answer 1

There is a very simple solution using string representation of numbers

    string = function(f){ // returns string representation of an object or number
        return f+"";
    }
    fPart = function(f){ // returns the fraction part (the part after the '.') of a number
        str = string(f);
        return str.indexOf(".")<0?"0":str.substring(str.indexOf(".") + 1);
    }
    wPart = function(f){ // returns the integer part (the part before the '.') of a number
        str = string(f);
        return str.indexOf(".")<0?str:str.substring(0, str.indexOf(".")); // possibility 1
        //return string(f - parseInt(fPart(f))); // just substract the fPart
    }

    power = function(base, exp){
        var tmp = base;
        while(exp>1){
            base*=tmp;
            --exp;
        }
        return base;
    }

    getFraction = function(f){ // the function
        var denominator = power(10, fPart(f).length), numerator = parseInt(fPart(f)) + parseInt(wPart(f))*denominator;
        return "[ " + numerator + ", " + denominator + "]";
    }

    console.log(getFraction(987.23));

which will just check how many numbers are in the fraction and then expands the fraction of f/1 until f is an integer. This can lead to huge fractions, so you can reduce it by dividing both numerator and denominator by the greatest common divisor of both, e.g.

    // greatest common divisor brute force
    gcd = function(x,y){
        for(var i = Math.min(x, y);i>0;i--) if(!(x%i||y%i)) return i;
        return 1;
    }