JS 中判断 undefined
var sugang =undefined;
if(typeof (sugang) =='undefined'){
alert("sugang is undefined")
}
JS 中判断 null
var sugang = null;
if (!sugang&& typeof(sugang)!='undefined && sugang!=0)
{
alert('sugang is null');
}
判断字符串是否为空
var sugang2=" ";
if(sugang2.trim().length==0){
alert("sugang2 是空字符串")
}
判断是否是空对象
var sugang3={};
if(JSON.stringify(sugang3)=="{}"){
alert("sugang2 是空对象")
}