Calculating a fraction from a double in javascript

The following code will allow you to calculate a fraction in javascript

 function getFraction(dblValue, dblTolerance)
    {
        var f0 = 1 / dblValue;

        var f1 = 1 / (f0 - Math.floor(f0));

        var a_t = Math.floor(f0);

        var a_r = Math.round(f0);

        var b_t = Math.floor(f1);

        var b_r = Math.round(f1);

        var c = Math.round(1 / (f1 - Math.floor(f1)));

        if (Math.abs(1.0 / a_r - dblValue) <= dblTolerance)
        {
            return [1, a_r];
        }
        else if (Math.abs(b_r / (a_t * b_r + 1.0) - dblValue) <= dblTolerance)
        {
            return [b_r, a_t * b_r + 1];
        }
        else {
            return [c * b_t + 1, c * a_t * b_t + a_t + c];

        }
    }

For example the following code examples give you a numerator and a denominator

console.log(getFraction(0.75,0.02));
/*[3, 4]*/
/***********************************/

console.log(getFraction(0.5,0.02));
/*[1, 2]*/
/***********************************/

console.log(getFraction(0.25,0.02));
/*[1, 4]*/
/***********************************/

console.log(getFraction(0.33,0.02));
/*[1, 3]*/
/***********************************/

Hope that's of use to somebody!