Date string parser

dateStringParser.js

function toDate(str) {
    
    // To map months to their numeric equivalent
    var months = {
        January   : 0,
        Feburary  : 1,
        March     : 2,
        April     : 3,
        May       : 4,
        June      : 5,
        July      : 6,
        August    : 7,
        September : 8,
        October   : 9,
        November  : 10,
        December  : 11
    };

    // Break up the date string with RegEx
    // Day, Month, Date, Year, Hour:Minute:Second
    var arry = str.match(/(\w+) (\w+) (\d+) (\d{4}) (\d{2}):(\d{2}):(\d{2}).*GMT([+-]\w{4})?/);
    
    // Parse the values as numbers
    var month  = months[arry[2]];
    var date   = Number(arry[3]);
    var year   = Number(arry[4]);
    var hour   = Number(arry[5]);
    var minute = Number(arry[6]);
    var second = Number(arry[7]);
    
    // Invert the offset, get as hours
    var GMT    = Number(arry[8]) / -100;
    
    // Convert everything to equivalent in seconds
    var sum = second + (minute*60) + (hour*60*60) + (date*24*60*60) + (monthToDays(month)*24*60*60) + (yearToDays(year)*24*60*60) + (GMT*60*60);
    
    return sum * 1000;
    
    // Helper to get number of days in the year preceding a month
    function monthToDays(month) {
        var numDays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        var days = 0;
        for (var i = 0; i < month; i++) {
            days += numDays[i];
        }
        return days;
    }
    
    // Helper to get the number of days in years preceding the current year
    function yearToDays(year) {
        var years = year - 1970;
        var days = years * 365;
        // Todo: Investigate magic `1`
        var leapDays = Math.floor(years / 4) - 1;
        return days + leapDays;
    }
}

// Test
var dateString = new Date().toString();
var seconds = toDate(dateString);
var calcDate = new Date(seconds).toString();

if (dateString === calcDate) {
    console.log('It works!');
} else {
    console.log('You found an edge case!', dateString);
}