Javascript – How to replace captured groups only

Using regular expressions is probably the best way. You can see a bunch of tests here (taken from chromium)

function validateEmail(email) {
    const 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(String(email).toLowerCase());
}

Here's the example of regular expresion that accepts unicode:

const re = /^(([^<>()[\]\.,;:\s@\"]+(\.[^<>()[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})$/i;

But keep in mind that one should not rely only upon JavaScript validation. JavaScript can easily be disabled. This should be validated on the server side as well.

Here's an example of the above in action:

function validateEmail(email) {
  const 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);
}

function validate() {
  const $result = $("#result");
  const email = $("#email").val();
  $result.text("");

  if (validateEmail(email)) {
    $result.text(email + " is valid :)");
    $result.css("color", "green");
  } else {
    $result.text(email + " is not valid :(");
    $result.css("color", "red");
  }
  return false;
}

$("#email").on("input", validate);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<label for=email>Enter an email address:</label>
<input id="email">
<h2 id="result"></h2>

Note: Using stopPropagation is something that should be avoided as it breaks normal event flow in the DOM. See this CSS Tricks article for more information. Consider using this method instead.

Attach a click event to the document body which closes the window. Attach a separate click event to the container which stops propagation to the document body.

$(window).click(function() {
  //Hide the menus if visible
});

$('#menucontainer').click(function(event){
  event.stopPropagation();
});