自定义JSON.stringify方法，兼容老版本浏览器

/**
 * JSON 值可以是：
 * 数字（整数或浮点数）
 * 字符串（在双引号中）
 * 逻辑值（true 或 false）
 * 数组（在方括号中）
 * 对象（在花括号中）
 * null
 */

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;
		}
	
		switch (Object.prototype.toString.call(val)) {
			case '[object Array]': // 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;
				
			case '[object Date]': // date
				return '"' + (val.toJSON ? val.toJSON() : val.toString()) + '"';
	
			case '[object RegExp]': // regular expression
				return "{}";
	
			case '[object Object]': // 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;
		}
	}
}

// 测试代码
console.log('Number');
var number = json.stringify(8);
console.log('stringify:',typeof number,number);
//console.log(JSON.parse(number));
//console.log(number === JSON.stringify(8));
console.log('-----------------------');

console.log('Boolean');
var boolean = json.stringify(true);
console.log('stringify:',typeof boolean,boolean);
//console.log(JSON.parse(boolean));
//console.log(boolean === JSON.stringify(true));
console.log('-----------------------');

console.log('Null');
var _null = json.stringify(null);
console.log('stringify:',typeof _null,_null);
//console.log(JSON.parse(_null));
//console.log(_null === JSON.stringify(null));
console.log('-----------------------');

console.log('Undefined');
var _undefined = json.stringify(undefined);
console.log('stringify:',typeof _undefined,_undefined);
//console.log(JSON.parse(_undefined));
//console.log(_undefined === JSON.stringify(undefined));
console.log('-----------------------');

console.log('String');
var string = json.stringify('abc123');
console.log('stringify:',typeof string,string);
//console.log(JSON.parse(string));
//console.log(string === JSON.stringify('abc123'));
console.log('-----------------------');

console.log('Array');
var theArray = [1,undefined,function () {},'a'];
var array = json.stringify(theArray);
console.log('stringify:',typeof array,array);
//console.log(JSON.parse(array));
//console.log(array === JSON.stringify(theArray));
console.log('-----------------------');

console.log('Function');

function fnTest() {
	console.log('function stringify');
}
var func = json.stringify(fnTest);
console.log('stringify:',typeof func,func);
//  console.log(JSON.parse(func));
//console.log(func === JSON.stringify(fnTest));
console.log('-----------------------');

console.log('Object');
var objTest = json.stringify({
	a: 1
});
console.log('stringify',typeof objTest,objTest);
//console.log(objTest === JSON.stringify({
//	a: 1
//}));
console.log('-----------------------');

console.log('RegExp');
var RegExp = json.stringify(/^a$/g);
console.log('stringify',typeof RegExp,RegExp);
//console.log(RegExp === JSON.stringify(/^a$/g));
console.log('-----------------------');

console.log('Date');
var theDate = new Date();
var date = json.stringify(theDate);
console.log('stringify',typeof date,date);
//console.log(date === JSON.stringify(theDate));
console.log('-----------------------');