原生Json.stringify的写法，将json对象转成json字符串

var json = {  
			   	 stringify: function (val) {  
			        var stringify = '',  
			            curVal;  
			  
			        if (val === null) {     // null  
			            return String(val);  
			        }  
			          
			        switch (typeof val) {  
			            case 'number': // number  
			            case 'boolean': // boolean  
			                return String(val);  
			      
			            case 'string': // string  
			                return '"' + val + '"';  
			              
			            case 'undefined': // undefined  
			            case 'function': // function  
			                return undefined;  
			        }  
					if(val.constructor == Array){
						 stringify += '[';  
			      
			                for (var i = 0, len = val.length - 1; i < len; i++) {  
			                    curVal = json.stringify(val[i]);  
			                    stringify += (curVal === undefined ? null : curVal) + ",";  
			                }  
			                stringify += json.stringify(val[i]);  
			      
			                stringify += ']';  
			                return stringify;  
					}else if(val.constructor == Object){
						       stringify += '{';  
			      
			                for (var i in val) {  
			//                  if (val.hasOwnProperty(i)) {  
			                        curVal = json.stringify(val[i]);  
			                        if (curVal !== undefined) {  
			                            stringify += '"' + i + '":' + curVal + ',';  
			//                      }  
			                    }  
			                }  
			      
			                stringify = stringify.slice(0, -1);                
			                stringify += '}';  
			                return stringify;  
					}else if(val.constructor == Date){
						
						return '"' + (val.toJSON ? val.toJSON() : val.toString()) + '"';  
					}else if(val.constructor == RegExp){
						return "{}";
					}
			    }  
			} var json = {  
			   	 stringify: function (val