reliable-round/index.js

A rounding library for JavaScript that behaves predictably (unlike Math.round, Math.floor, Math.ceil).

"use strict";
exports.__esModule = true;
function round(value, decimalPlacesToRoundTo) {
    if (decimalPlacesToRoundTo === void 0) { decimalPlacesToRoundTo = 0; }
    var isNegative = value < 0;
    var numberAsString = numberToString(value);
    var parts = numberAsString.split('.');
    var integerPart = parts[0].replace('-', '');
    var decimalPart = parts[1] || '';
    if (decimalPart === '') {
        return value;
    }
    var integerDigits = ['0'].concat(integerPart.split(''));
    var decimalDigits = decimalPart.split('').concat(['0']);
    var allDigits = integerDigits.concat(decimalDigits);
    var startIndex = Math.min(integerDigits.length + decimalPlacesToRoundTo, allDigits.length - 1);
    var stopRoundingAtIndex = integerDigits.length - 1 + decimalPlacesToRoundTo;
    if (startIndex < allDigits.length - 1) {
        allDigits.splice(startIndex + 1, decimalDigits.length - 1);
    }
    var carry = 0;
    for (var index = startIndex; index > -1; index--) {
        var digit = parseInt(allDigits[index], 10);
        var newDigit = void 0;
        if (index > stopRoundingAtIndex) {
            newDigit = 0;
            carry = digit + carry >= 5 ? 1 : 0;
        }
        else {
            newDigit = (digit + carry) % 10;
            carry = digit + carry >= 10 ? 1 : 0;
        }
        allDigits[index] = newDigit.toString();
    }
    allDigits.splice(integerDigits.length, 0, '.');
    var absoluteResult = parseFloat(allDigits.join(''));
    var result = isNegative ? -absoluteResult : absoluteResult;
    return result;
}
exports.round = round;
// tslint:disable-next-line:max-line-length
// Sourced from: https://stackoverflow.com/questions/1685680/how-to-avoid-scientific-notation-for-large-numbers-in-javascript/46545519#46545519
function numberToString(value) {
    var tempValue = value;
    var numStr = String(tempValue);
    if (Math.abs(tempValue) < 1.0) {
        var e = parseInt(tempValue.toString().split('e-')[1], 10);
        if (e) {
            var negative = tempValue < 0;
            if (negative) {
                tempValue *= -1;
            }
            tempValue *= Math.pow(10, e - 1);
            // tslint:disable-next-line:prefer-array-literal
            numStr = '0.' + (new Array(e)).join('0') + tempValue.toString().substring(2);
            if (negative) {
                numStr = '-' + numStr;
            }
        }
    }
    else {
        var e = parseInt(tempValue.toString().split('+')[1], 10);
        if (e > 20) {
            e -= 20;
            tempValue /= Math.pow(10, e);
            // tslint:disable-next-line:prefer-array-literal
            numStr = tempValue.toString() + (new Array(e + 1)).join('0');
        }
    }
    return numStr;
}
exports.numberToString = numberToString;