JS->JS邮箱格式判断

function ischeck(){

var companyemail = document.getElementById("companyemail").value;
            if (companyemail != "") {
                var reg = /^([a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+((\.[a-zA-Z0-9_-]{2,3}){1,2})$/;
                flag = reg.test(companyemail);
                if (!flag) {
                    alert("邮箱格式不正确！");
                    document.getElementById("companyemail").focus();
                    return false;
                }
            }

}