1.操作符两边如果有对象，将其转换成number；如果无法转换成number，则将其转换成string。
2.经过转换后，如果操作符两边均为string，则进行字符串比较；否则，只要有一边出现number，则进行数值比较。
3.如果操作符两边出现NaN，返回false。
4.0与-0相等。
实验
代码如下:
//In comparison, Date object is converted to number
var d = new Date();
var s1 = "Thu Mar 27 2008 14:57:11 GMT+0800 (CST)";
var s2 = "Thu Mar 27 2099 14:57:11 GMT+0800 (CST)";
var n1 = d.valueOf() - 1000;
var n2 = d.valueOf() + 1000;
console.log(d > s1);//false, d is converted to number, and that number is further converted to string. It is a string comparison here.
console.log(d > s2);//false
console.log(d > n1);//true
console.log(d > n2);//false
console.log("11" > 3);//true
