Send message to browser

Question

I need to send a message like this to the browser:

How can I do on a site made with C#, ASP.NET and Webforms?

Answer 1

If you are creating a basic page or are studying the principle would be to create a link to trigger the event (not necessarily needing ASP.NET) in html:

<a href="javascript:void(0);" onclick="alert('Olá mundo!')">Clique aqui</a>

You can create a simple button as well:

<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="alert('Olá mundo!');"/>

Note that the asp:Button is used to control server-side events (which is accompanied by a <form>)

To insert a simple javascript into an html page, the basics would be this:

<script type="text/javascript">
alert('Olá mundo!');
</script>

You can also use files .js, as an example:

<script type="text/javascript" src="foo.js"></script>

In foo.js will contain:

alert('Olá mundo!');

I believe that here the principle is more the issue of "html", but if you are interested (and I’m sure that if in the future you want to learn more about the advanced controls of .net), I recommend that you follow the Gypsy tip and read about the ScriptManager, follows link from the documentation:

• https://msdn.microsoft.com/pt-br/library/system.web.ui.scriptmanager(v=vs.110). aspx

The main types of dialog windows on web pages

• The window.alert or simply alert, is an event that displays a simple dialog window with a text message (and does no more action), example:

  function meuEvento() {
      alert("Olá");
  }

  <button onclick="meuEvento();">Clique aqui</button>

• The window.confirm or simply confirm, is an event that displays a dialog window with a text message and two buttons, one to confirm an action and one to cancel the action (note that clicking close will be the same as clicking cancel), this event returns a boolean value, being true click on Ok or false click on Cancel (cancel):

  function meuEvento() {
      if (window.confirm("Você quer confirmar ou cancelar?")) {
          alert("Você clicou em Ok");
      } else {
          alert("Você clicou em Cancelar ou em Fechar");
      }
  }

  <button onclick="meuEvento();">Clique aqui</button>

• The window.prompt or simply prompt, is an event that displays a dialog window with a text message, a text field and a button to confirm and another to cancel. This method return a string, if you click cancel (or close) a null instead of string:

  function meuEvento() {
      var resposta = window.prompt("Qual o seu nome?");
  
      if (resposta !== null) {
          alert("Seu nome é:" + resposta);
      } else {
          alert("Você clicou em Cancelar ou em Fechar");
      }
  }

  <button onclick="meuEvento();">Clique aqui</button>

• The event window.onbeforeunload is what makes the "effect" of the image you posted, this event expects a return, chance has not return it will act normally by closing the window and ignoring other events, while using return on it you will be adding a check to the user if he wants to leave a particular page, this event is triggered in Passwords, sending form, reload the page, when you close a tab or window, example as quoted by Gypsy of this response from Soen:

  window.onbeforeunload = function(e) {
      var msg = "Quer mesmo sair desta página?";
      e = e || window.event;
  
      // Pro IE e Firefox anterior a versão 4
      if (e) {
          e.returnValue = msg;
      }
  
      // Para Safari e Chrome
      return msg;
  }

  <button onclick="window.location.reload();">Recarregar página</button>
  <br>
  <a href="?">Páginar</a>

Note that there are other window events, such as popups and modals, but the types of dialogs are basically those cited here, if you want to see more methods used by the object window, you can have a look at the Mozilla documentation:

• https://developer.mozilla.org/en-US/docs/Web/API/Window

Answer 2

You can use the onbeforeunload javascript, it presents this window that asks if the user really wants to leave the page.

window.onbeforeunload = function(e){
   e = e || window.event, msg = 'Você tem certeza que deseja sair dessa página?';
   if (e) e.returnValue = msg;
   return msg;
};