JavaScript code for parsing an ISO 8601 string to a JavaScript Date instance.

iso8601_parse_datetimes.js

/*
 * dateFromISODatetime creates a JavaScript date from a string that adheres to 
 * ECMAScript's specified syntax:
 *  Zulu/UTC time:   
 *      YYYY-MM-DDTHH:mm:ss.sssZ  
 *  Specified time zone offset: 
 *      YYYY-MM-DDTHH:mm:ss.sss±HH:mm
 *  Local time (no time zone specification): 
 *      YYYY-MM-DDTHH:mm:ss.sss
 */
let dateFromISODatetime = function (isoString) {  
    const DATE_REGEX =   /^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2}.\d{3})(Z|(?:(?:-|\+)\d{2}:\d{2}))?$/;

    const MIN_YEAR =1;
    const MAX_YEAR = 9999;
    const MIN_MONTH = 1;
    const MAX_MONTH = 12;
    const MIN_DAY = 1;
    const MIN_HOUR = 0;
    const MAX_HOUR = 24;
    const MIN_MINUTE = 0;
    const MAX_MINUTE = 59;
    const MIN_SECOND = 0;
    const MAX_SECOND = 60;

    const matches = isoString.match(DATE_REGEX);
    if (matches === null) {
        throw new SyntaxError("Invalid date attribute");
    }

    let year = parseInt(matches[1]);
    if (year < MIN_YEAR || year > MAX_YEAR) {
        throw new RangeError(`Year must be >= ${MIN_YEAR} and <= ${MAX_YEAR}`);
    }

    let month = parseInt(matches[2]);
    if (month < MIN_MONTH || month > MAX_MONTH) {
        throw new RangeError(`Month must be >= ${MIN_MONTH} and <= ${MAX_MONTH}`);
    }

    let dayCount = monthDayCount(month, year);
    let day = parseInt(matches[3]);
    if (day < MIN_DAY || day > dayCount) {
        throw new RangeError(`Day must be >= ${MIN_DAY} and <= ${dayCount}`);
    }

    let hour = parseInt(matches[4]);
    if (hour < MIN_HOUR || hour > MAX_HOUR) {
        throw new RangeError(`Hour must be >= ${MIN_HOUR} and <= ${MAX_HOUR}`);
    }

    let minute = parseInt(matches[5]);
    if (minute < MIN_MINUTE || minute > MAX_MINUTE) {
        throw new RangeError(`Minutes must be >= ${MIN_MINUTE} and <= ${MAX_MINUTE}`);
    }

    let second = parseInt(matches[6]);
    if (second < MIN_SECOND || second > MAX_SECOND) {
        throw new RangeError(`Seconds  must be >= ${MIN_SECOND} and <= ${MAX_SECOND}`);
    }

    return new Date(isoString);
}