js邮箱验证

/* 1、必须有@ index("@")==-1【没找到】
2、必须有.
3、@必须在.之前
4、@前必须有字符
5、.后边必须有字符
6、@和.之间必须有字符
7、.在@后边出现次数不能超过2次*/
var email = prompt("请输入邮箱", "232@qq.com");
if (email.indexOf(".") != -1) {
var atindex = email.indexOf("@");
var lastatindex = email.lastIndexOf("@");
var pointindex = email.indexOf(".");
var lastpointindex = email.lastIndexOf(".");
var str1;
var str2;
//判断@出现的次数
if (atindex != lastatindex)
str1 = email.substring(atindex, lastatindex);
else
str1 = "";
//判断点出现的次数
if (pointindex != lastpointindex)
str2 = email.substring(pointindex, lastpointindex);
else
str2 = "";
//条件判断
if (pointindex < atindex) {
alert("@必须在.之前");
}
else if (atindex == 0)
alert("@前必须有字符");
else if (pointindex == lastpointindex.length - 1)
alert(".后边必须有字符");
else if (pointindex == atindex + 1)
alert("@和.之间必须有字符");
else if (str1.indexOf("@") != -1)
alert("@不能出现2次");
else if (str2.indexOf(".") != -1)
alert(".不能出现2次");
else
alert("邮箱格式正确！");
}
else
alert(".和@都必须包含");