//asdfasdfasdf未定义
(1)
if(asdfasdfasdf){
alert(1);
}
结果:IE报错,asdfasdfasdf未定义,try 捕捉不了。
(2)
if(typeof asdfasdfasdf){
alert(1);
}
结果:输出1
(3)
if(typeof asdfasdfasdf == undefined){
alert(1);
}
结果:输出1
?? asdfasdfasdf 为什么不能转化成bool类型的false