Improved Code for Javascript Decimal to Fraction

This post improves the code at “Code of the Day Javascript Decimal to fraction” by using Euclid’s Algorithm to find the Great Common Factor or GCF, aka GCD. This method provides a speed up of 10x when compared to the original algorithm posted.

Code

/**
*@function gcd (aka Euclid's algorithm)
*@purpose returns the greatest common factor between two numbers;
*/
function gcd(a, b) {
    return (b) ? gcd(b, a % b) : a;
}
/**
*@function dec2Frac
*@purpose returns a decimal as a fraction.
*/
var dec2Frac = function ( num ) {
	var top = num.toString().replace(/\d+[.]/, '');
	var bot = Math.pow(10, top.length);
	if (num > 1) {
		top = +top + Math.floor(num) * bot;
	}
	var x = gcd(top, bot);
	return (top / x) + "/" + (bot / x);
};

Usage

dec2Frac( 1.24325 ) // returns "4973/4000"
dec2Frac( 2.45 ) // returns "49/20"

Speed Test between Version 1 and 2 of dec2Frac()

//@requires Firebug or Chrome Developer Tools
//The following code test the speed difference between the Version 1 and 2 of dec2Frac.
function gcd(a, b) {
    return (b) ? gcd(b, a % b) : a;
}
var dec2FracV2 = function (d) {
	var top = d.toString().replace(/\d+[.]/, '');
	var bot = Math.pow(10, top.length);
	if (d > 1) {
		top = +top + Math.floor(d) * bot;
	}
	var x = gcd(top, bot);
	return (top / x) + "/" + (bot / x);
};
function dec2FracV1(d) {
    var df = 1, top = 1, bot = 1;
    var limit = 1e5; //Increase the limit to get more precision.
 
    while (df != d && limit-- > 0) {
        if (df < d) {
            top += 1;
        }
        else {
            bot += 1;
            top = parseInt(d * bot, 10);
        }
        df = top / bot;
    }
    return top + '/' + bot;
}
var getRandomNum = function (i, decLen) {
	return (Math.random() * (i || 1)).toFixed(decLen);
};
 
var runTest = function ( funcName ) {
	var func = { "V1": dec2FracV1, "V2": dec2FracV2 }[ funcName ];
	var i = 1000;
	while (i--) {
		num = getRandomNum(10, 4);
		var x = func(num);
		if (num != eval(x)) {
			console.warn("ERROR: Function %s, The fraction %s != %s", funcName, num, x);
		}
	}
};
console.time( 'V1' );
runTest( "V1" );
console.timeEnd( 'V1' );
 
console.time( 'V2' );
runTest( "V2" );
console.timeEnd( 'V2' );

Chrome Result:
V1: 11628ms
V2: 185ms

Try the test out yourself
jsbin.com

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