Javascript IRR (Internal rate of return) Formula Accuracy

Question

I\'m using a IRR function in javascript to create calculation a that is done in excel using its own IRR function. The problem is mine is little off and I have no idea why. Here\

Answer 1

This might be a better way of writing the calculation. This allows the code to calculate instances of negative IRR or IRR above 100%.

        var IRRval = [];

        IRRval.push(-financed);
            for (i = 0; i < period; i++) {
            IRRval.push(rental);
        }
        var IRR = IRRCalc(IRRval, 0.001) * 0.01;

        function IRRCalc(CArray) {
            var r = 0
            min = -1.0;
            max = 10000.0;
            do {
                guest = (min + max) / 2;
                NPV = 0;
                for (var j = 0; j < CArray.length; j++) {
                    NPV += CArray[j] / Math.pow((1 + guest), j);
                }
                if (NPV > 0) {
                    min = guest;
                }
                else {
                    max = guest;
                }
                r++
            } while (r < 100);
            return guest * 100
        }