如何判断输入的邮箱是否正确

var btn = document.getElementById('btn');

var txt = document.getElementById('txt');

 

 

btn.onclick = function(){

var str = txt.value;

var reg = /^[a-zA-Z0-9]+@[a-z0-9]{2,5}.[a-z]{2,3}(.[a-z]{2,3})?$/;

var result = reg.test(str);

if(result){

alert('是正确的邮箱');

}else{

alert('您输入的邮箱有误')

}

}