How do you automatically set the focus to a textbox when a web page loads?

If you're using jquery:

$(function() {
  $("#Box1").focus();
});

or prototype:

Event.observe(window, 'load', function() {
  $("Box1").focus();
});

or plain javascript:

window.onload = function() {
  document.getElementById("Box1").focus();
};

though keep in mind that this will replace other on load handlers, so look up addLoadEvent() in google for a safe way to append onload handlers rather than replacing.

You need to use javascript:

<BODY onLoad="document.getElementById('myButton').focus();">

@Ben notes that you should not add event handlers like this. While that is another question, he recommends that you use this function:

function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}

And then put a call to addLoadEvent on your page and reference a function the sets the focus to you desired textbox.

Using plain vanilla html and javascript

<input type='text' id='txtMyInputBox' />


<script language='javascript' type='text/javascript'>
function SetFocus()
{
    // safety check, make sure its a post 1999 browser
    if (!document.getElementById)
    {
        return;
    }

    var txtMyInputBoxElement = document.getElementById("txtMyInputBox");

    if (txtMyInputBoxElement != null)
    {
        txtMyInputBoxElement.focus();
    }
}
SetFocus();
</script>

For those out there using the .net framework and asp.net 2.0 or above, its trivial. If you are using older versions of the framework, you'd need to write some javascript similar to above.

In your OnLoad handler (generally page_load if you are using the stock page template supplied with visual studio) you can use:

C#

protected void PageLoad(object sender, EventArgs e)
{
    Page.SetFocus(txtMyInputBox);
}

VB.NET

Protected Sub PageLoad(sender as Object, e as EventArgs)

    Page.SetFocus(txtMyInputBox)

End Sub

(* Note I removed the underscore character from the function name that is generally Page_Load since in a code block it refused to render properly! I could not see in the markup documentation how to get underscores to render unescaped.)

Hope this helps.

<html>  
<head>  
<script language="javascript" type="text/javascript">  
function SetFocus(InputID)  
{  
   document.getElementById(InputID).focus();  
}  
</script>  
</head>  
<body onload="SetFocus('Box2')">  
<input id="Box1" size="30" /><br/>  
<input id="Box2" size="30" />  
</body>  
</html>  

As a general advice, I would recommend not stealing the focus from the address bar. (Jeff already talked about that.)

Web page can take some time to load, which means that your focus change can occur some long time after the user typed the pae URL. Then he could have changed his mind and be back to url typing while you will be loading your page and stealing the focus to put it in your textbox.

That's the one and only reason that made me remove Google as my start page.

Of course, if you control the network (local network) or if the focus change is to solve an important usability issue, forget all I just said :)

It is possible to set autofocus on input elements

<input type="text" class="b_calle" id="b_calle" placeholder="Buscar por nombre de calle" autofocus="autofocus">

Adjusted my answer from Dave1010 above as JavaScript backup didn't work for me.

<input type="text" id="my-input" />

And the Javascipt backup check:

if (!(document.getElementById("my-input").hasAttribute("autofocus"))) {
    document.getElementById("my-input").focus();
}