电子邮件验证始终失败

Question

I copied most popular validation method from different StackOverflow answers, but the problem email always appears to be not valid. So that second condition is never executed. What am I understanding wrong?

function validateEmail(email) {
  var re = /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
  return re.test(email);
}
var emailaddress = document.getElementById("email_input").value;
$("#email_input").keydown(function(emailaddress) {
  if (!validateEmail(emailaddress)) {
    $('#enter_valid_email').remove()
    $('<span class="enter_smth_valid" id="enter_valid_email">Enter valid email</span>').insertAfter('#email_input')
  } else {
    alert();
    $('#enter_valid_email').remove()
  }
});

Answer 1

The function passed to keydown is an event handler - it receives an event object as the first parameter passed to it (if you need it). You are treating that as the text itself. A small change will fix the problem:

$("#email_input").keydown(function() {
   var emailAddress = $(this).val();
  if (!validateEmail(emailAddress )) {
    $('#enter_valid_email').remove()
    $('<span class="enter_smth_valid" id="enter_valid_email">Enter valid email</span>').insertAfter('#email_input')
  } else {
    alert();
    $('#enter_valid_email').remove()
  }
});

You can also remove this line above that - it does nothing:

var emailaddress = document.getElementById("email_input").value;