sumArgs

sumArgs.js

function getPrecision(num) {
    var split = (num + "").split(/([\.e\-]{1,2})/);
    var i, len, token, next, nextNum, precision;
    for (precision = 0, i = 1, len = split.length; i < len; i += 1) {
        token = split[i];
        next = split[i + 1];
        nextNum = +next;
        if (token === ".") {
            precision += next.length;
        } else if (token === "e-") {
            precision += i > 1 ? nextNum + 1 : nextNum;
            break;
        }
    }
    return precision;
}

function getMaxPrecision(arr) {
    var i, len, precision, max;
    for (max = 0, i = 0, len = arr.length; i < len; i += 1) {
        precision = getPrecision(arr[i]);
        max = (precision > max) ? precision : max;
    }
    return max;
}

function sumArgs() {
    var args = Array.prototype.slice.call(arguments);
    var max = getMaxPrecision(args);
    var pow = Math.pow(10, max);
    var i, len, sum, arg;
    for (sum = 0, i = 0, len = args.length; i < len; i += 1) {
        arg = args[i];
        sum += isNaN(arg) ? 0 : (arg * pow);
    }
    return sum / pow;
}

console.assert(getPrecision(1) === 0, 
    "no decimal or e-"); 
console.assert(getPrecision(1.1234567890) === 9, 
    "zeros are dropped, just decimal");
console.assert(getPrecision(1.1234567890123456) === 16, 
    "longest without rounding");
console.assert(getPrecision(0.1) === 1);
console.assert(getPrecision(0.12345678901234567) === 17, 
    "longest without rounding");
console.assert(getPrecision(0.0000000001) === 10, 
    "no decimal, just e-");
console.assert(
  getPrecision(
    0.00000000000000000000000000000000000000000000000000000123456789012345678
  ) === 71
);
console.assert(sumArgs(0.00002, 0.00001, 0.1, 0.02) === 0.12003);
console.assert(getPrecision(Math.min()) === 0, 
    "Infinity");
console.assert(getPrecision(1e309) === 0, 
    "Infinity");
console.assert(getPrecision(1e-324) === 0, 
    "Infinity precision (in Chrome)");
console.assert(getPrecision(1e-323) === 323, 
    "slightly less than Infinity (in Chrome)");