Function that parses stuff to milliseconds

ms.js

/* inspiration from Jan-Marten de Boer´s Time.js, https://github.com/johmanx10/Time.js */
var ms = (function () {
    'use strict';

    var second = 1000,
        minute = second*60,
        hour   = minute*60,
        day    = hour*24,
        //week   = day*7,
        //year   = second*3.154e7,// According to Wolfram|Alpha
        //month  = ~~(year/12),   // ~~ == parseInt
        typeOf,
        parse;

    typeOf = (function ( classNames ) {
        // a better typeof

        var className, i, classTypeMap;

        classNames = classNames.replace(/\s+/g, ' ').split(' ');
        i = classNames.length;
        classTypeMap = {};

        while ( ( className = classNames[--i] ) ) {
            classTypeMap[ '[object ' + className + ']' ] = className.toLowerCase();
        }

        return function ( o ) {
            if ( 0 === arguments.length ) {
                o = this;
            }

            return null == o ? o + '' : classTypeMap[Object.prototype.toString.call( o )] || 'object';
        };
    } ('Date Number String'));// Arguments Array Boolean Date Function Number RegExp String

    parse = (function () {
        var re = /(\d+)(d|h|min|s|ms)/g,
            fn = {
                'd': function ( i ) {
                    return i * day;
                },
                'h' : function ( i ) {
                    return i * hour;
                },
                'min' : function ( i ) {
                    return i * minute;
                },
                's' : function ( i ) {
                    return i * second;
                },
                'ms' : function ( i ) {
                    return 1 * i;
                }
            };

        return function ( s ) {
            var ms = Date.parse( s ),
                match, value, unit;

            if ( isNaN(ms) ) {
                s = s.replace(/\s+/g, '');
                ms = 0;
                while ( null != (match = re.exec(s)) ) {
                    value = match[1];
                    unit = match[2];
                    ms += fn[unit] && ~~fn[unit]( value );// ~~ == parseInt
                }
            }

            return ms;
        };
    } ());

    return function ( o ) {
        var ms;

        // o could be of type Date, Number or String
        // String can be either something that is parsable by Date.parse OR a string with SI units and non-SI
        // units accepted for use with the SI, see http://en.wikipedia.org/wiki/Non-SI_units_mentioned_in_the_SI
        //
        // e.g. '1h 30min 30s' == 1 hour, 30 minutes and 30 seconds
        // whitespace is not required -> '1h30min30s' also works

        //o = new Date(2012, 0, 23, 15, 20, 0, 0);

        switch ( typeOf(o) ) {
            case 'string':
                ms = parse( o );
                break;
            case 'date':
                ms = o - new Date();
                break;
            case 'number':
                ms = o;
                break;
            default:
                // throw 'Not valid input';
        }

        return Math.max(0, ms);
    };
} ());