jQuery addClass example

Change class name on click in jQuery

HTML

<form class="form">
 <input type="text" id="username" name="username" />
 <input type="text" id="password" name="password" />
 <input type="submit" id="submit" value="Войти" disabled />
</form>

JavaScript

$("#username, #password").on("input", function() {
  if($("#username").val().length > 5 && $("#password").val().length > 5) {
    $("#submit").prop("disabled", false);
  } else {
    $("#submit").prop("disabled", true);
  }
});