jQuery方法扩展：type, toJSON, evalJSON

jQuery居然都没有JSON的decode和encode，精确类型判断也没有，囧……自己动手写吧！不过这些东西在网上都已经有很好的版本了，自己也不用太费脑筋，拿来用吧！类型判断在这里有一段很好的代码：http://lucassmith.name/pub/typeof.html，JSON的decode和encode就直接用Mootools的吧！（不过Mootools里面的JSON.encode方法还不够完美，我作了一些完善。）

/**
* extension of JSON, type for jQuery
* AUTHOR: xushengs@gmail.com
* LICENSE: http://www.opensource.org/licenses/mit-license.php
* WEBSITE: http://ooboy.net/
*/
(function($) {
    // the code of this function is from
    // http://lucassmith.name/pub/typeof.html
    $.type = function(o) {
        var _toS = Object.prototype.toString;
        var _types = {
            'undefined': 'undefined',
            'number': 'number',
            'boolean': 'boolean',
            'string': 'string',
            '[object Function]': 'function',
            '[object RegExp]': 'regexp',
            '[object Array]': 'array',
            '[object Date]': 'date',
            '[object Error]': 'error'
        };
        return _types[typeof o] || _types[_toS.call(o)] || (o ? 'object' : 'null');
    };
    // the code of these two functions is from mootools
    // http://mootools.net
    var $specialChars = { '\b': '\\b', '\t': '\\t', '\n': '\\n', '\f': '\\f', '\r': '\\r', '"': '\\"', '\\': '\\\\' };
    var $replaceChars = function(chr) {
        return $specialChars[chr] || '\\u00' + Math.floor(chr.charCodeAt() / 16).toString(16) + (chr.charCodeAt() ％ 16).toString(16);
    };
    $.toJSON = function(o) {
        var s = [];
        switch ($.type(o)) {
            case 'undefined':
                return 'undefined';
                break;
            case 'null':
                return 'null';
                break;
            case 'number':
            case 'boolean':
            case 'date':
            case 'function':
                return o.toString();
                break;
            case 'string':
                return '"' + o.replace(/[\x00-\x1f\\"]/g, $replaceChars) + '"';
                break;
            case 'array':
                for (var i = 0, l = o.length; i < l; i++) {
                    s.push($.toJSON(o[i]));
                }
                return '[' + s.join(',') + ']';
                break;
            case 'error':
            case 'object':
                for (var p in o) {
                    s.push(p + ':' + $.toJSON(o[p]));
                }
                return '{' + s.join(',') + '}';
                break;
            default:
                return '';
                break;
        }
    };
    $.evalJSON = function(s) {
        if ($.type(s) != 'string' || !s.length) return null;
        return eval('(' + s + ')');
    };
})(jQuery);