比较运算
1
undefined>-1
一个是数值
先转化另一个为数,后台调用Number()方法
Number(undefined);//NaN
2
任何数值和NaN比较,false
null,undefined
null==undefined; //true
null!=undefined; //false null==0; //false
undefined==0;//false
3
typeof返回"字符串"!!
4
蛋疼的IE
function f(a,b){var i=a;}; console.log(typeof f);//function console.log(typeof ActiveXObject);//undefined var xmldom=new ActiveXObject('MSXML2.DOMDocument.6.0'); console.log(typeof xmldom);//object