DateTime.js

"use strict";
var DateTime = (function () {

    var monthNames = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
        dayNames = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

    function createDateTime(date) {
        return {
            get year() {
                return date.getUTCFullYear();
            },
            get monthName() {
                return monthNames[date.getUTCMonth()];
            },
            get month() {
                return date.getUTCMonth() + 1;
            },
            get day() {
                return dayNames[date.getUTCDay()];
            },
            get date() {
                return date.getUTCDate();
            },
            get ordinalDate() {
                var n = this.date;
                var suffix = "th";
                if (n < 4 || n > 20) {
                    suffix = ["st", "nd", "rd"][n % 10 - 1] || suffix;
                }
                return n + suffix;
            },
            get hours() {
                return date.getUTCHours();
            },
            get hours12() {
                return this.hours % 12 || 12;
            },
            get minutes() {
                return date.getUTCMinutes();
            },
            get seconds() {
                return date.getUTCSeconds();
            },
            get ampm() {
                return this.hours < 12 ? "am" : "pm";
            },
            get offset() {
                return date.getTime();
            },
            set year(v) {
                date.setUTCFullYear(v);
            },
            set month(v) {
                date.setUTCMonth(v - 1);
            },
            set monthName(v) {
                var index = monthNames.indexOf(v);
                if (index < 0) {
                    throw new Error("'" + v + "' is not a valid month name.");
                }
                date.setUTCMonth(index);
            },
            set day(v) {
                throw new Error("The property 'day' is readonly.");
            },
            set date(v) {
                date.setUTCDate(v);
            },
            set ordinalDate(v) {
                date.setUTCDate(+v.slice(0, -2));
            },
            set hours(v) {
                date.setUTCHours(v);
            },
            set hours12(v) {
                date.setUTCHours(v % 12);
            },
            set minutes(v) {
                date.setUTCMinutes(v);
            },
            set seconds(v) {
                date.setUTCSeconds(v);
            },
            set ampm(v) {
                if (!/^(am|pm)$/.test(v)) {
                    throw new Error("'" + v + "' is not 'am' or 'pm'.");
                }
                if (v !== this.ampm) {
                    date.setUTCHours((this.hours + 12) % 24);
                }
            },
            set offset(v) {
                date.setTime(v);
            },
            toString: function (formatString) {
                formatString = formatString || "YYYY-M-D H:m:s";
                return toString(this, formatString);
            }
        };
    }

    var formatAbbreviations = {
        YYYY: "year",
        YY: "shortYear",
        MMMM: "monthName",
        M: "month",
        dddd: "day",
        D: "date",
        Do: "ordinalDate",
        H: "hours",
        h: "hours12",
        m: "minutes",
        s: "seconds",
        a: "ampm"
    };
    var maxAbbreviationLength = 4;
    var formatPatterns = {
        year: /^-?[0-9]+/,
        monthName: /January|February|March|April|May|June|July|August|September|October|November|December/,
        month: /[1-9][0-9]?/,
        day: /Sunday|Monday|Tuesday|Wednesday|Thursday|Friday|Saturday/,
        date: /[1-9][0-9]?/,
        ordinalDate: /[1-9][0-9]?(st|nd|rd|th)/,
        hours: /[0-9]{1,2}/,
        hours12: /[0-9]{1,2}/,
        minutes: /[0-9]{1,2}/,
        seconds: /[0-9]{1,2}/,
        ampm: /am|pm/
    };


    function tokenize(formatString) {
        var tokens = [];
        for (var i = 0; i < formatString.length; i++) {
            var slice, propertyName;
            for (var j = maxAbbreviationLength; j > 0; j--) {
                slice = formatString.slice(i, i + j);
                propertyName = formatAbbreviations[slice];
                if (propertyName) {
                    tokens.push({ type: "property", value: propertyName });
                    i += j - 1;
                    break;
                }
            }
            if (!propertyName) {
                tokens.push({ type: "literal", value: slice });
            }
        }
        return tokens;
    }

    function toString(dateTime, formatString) {
        var tokens = tokenize(formatString);
        return tokens.map(function (token) {
            if (token.type === "property") {
                var value = dateTime[token.value];
                if (token.value === "minutes" || token.value === "seconds") {
                    value = ("00" + value).slice(-2);
                }
                return value;
            }
            return token.value;
        }).join("");
    }

    function parse(string, formatString) {
        var tokens = tokenize(formatString);
        var properties = {};
        tokens.forEach(function (token, i) {
            if (token.type === "literal") {
                var value = token.value,
                    slice = string.slice(0, value.length);
                if (slice !== value) {
                    throw new Error("String does not match format. Expected '" + slice + "' to equal '" + value + "'.");
                }
                string = string.slice(value.length);
            } else {
                var format = token.value,
                    pattern = formatPatterns[format],
                    match = string.match(pattern);
                if (!match || !match.length) {
                    throw new Error("String does not match format. Expected '" + string + "' to start with the pattern " + pattern + ".");
                }
                match = match[0];
                string = string.slice(match.length);
                properties[format] = match;
            }
        });
        var propertyOrder = ["seconds", "minutes", "hours12", "ampm", "hours", "ordinalDate", "date", "monthName", "month", "year"];
        var date = createDateTime(new Date(0));
        propertyOrder.forEach(function (property) {
            if (properties[property]) {
                date[property] = properties[property];
            }
        });
        return date;
    }

    return function (date, formatString) {
        if (date !== undefined) {
            if (date instanceof Date) {
                return createDateTime(date);
            }
            if (typeof formatString === "string") {
                return parse(date, formatString);
            }
            throw new Error(String(date) + " is not a Date object.");
        }
        return createDateTime(new Date());
    };
})();