Fixing the enter key in ASP.NET with jQuery

One of the fundamental problems with ASP.NET WebForms is the fact that you can only have one form per page. This jumps up and bites you when you have a set of fields and a button and you want the enter key to submit the form.

In ASP.NET 2.0 they came out with a “fix” for this. You can wrap your fields in a Panel and set the default button:

<asp:Panel ID="_pnlLogin" DefaultButton="_btnLogin" runat="server">
    UserName: <asp:TextBox ID="_txtUserName" runat="server" />
    Password: <asp:TextBox ID="_txtPassword" runat="server" />
    <asp:LinkButton ID="_btnLogin" Text="Login" runat="server"/>
</asp:Panel>

Some of you will know limitation here. This works with a Button, but not a LinkButton. Let’s see why.
Here is the resulting HTML:

<div id="_pnlLogin" onkeypress="javascript:return WebForm_FireDefaultButton(event, &amp;#x27;_btnLogin&amp;#x27;)">
    UserName: <input name="_txtUsername" type="text" id="_txtUsername" />
    Password: <input name="ctl00$mainContent$_txtPassword" type="text" id="_txtPassword" />
    <a id="_btnLogin" href="javascript:__doPostBack('_btnLogin','')">Login</a>
</div>

The Panel renders as a div, and on any key pressed will call WebForm_FireDefaultButton:

function WebForm_FireDefaultButton(event, target) {
    if (!__defaultFired && event.keyCode == 13 && !(event.srcElement && (event.srcElement.tagName.toLowerCase() == "textarea"))) {
        var defaultButton;
        if (__nonMSDOMBrowser) {
            defaultButton = document.getElementById(target);
        } else {
            defaultButton = document.all[target];
        }
        if (defaultButton && typeof(defaultButton.click) != "undefined") {
            __defaultFired = true;
            defaultButton.click();
            event.cancelBubble = true;
        if (event.stopPropagation) event.stopPropagation();
            return false;
        }
    }
    return true;
}

This method checks for the enter key and then calls click on the default button. All good except for one thing: the LinkButton renders as an “a” tag. Anchor tags don’t have a click() method unfortunately. At least not in Firefox.

So let’s fix it! I’ve recently been reading “Learning jQuery”
which is a great book on this cool javascript library. I’ll use jQuery instead of straight javascript as it is much easier to write cross browser code and it’s a lot more concise. Plus there are heaps of plugins for it, and it’s a pretty small download for your page.

I want to improve the markup of my page at the same time so I’ll try to minimise the amount of server controls I use and get rid of that inline javascript call. My new aspx looks like this:

<div class="form">
    UserName: <asp:TextBox ID="_txtUsername" runat="server" />
    Password: <asp:TextBox ID="_txtPassword" runat="server" />
    <asp:LinkButton ID="_btnLogin" Text="Login" runat="server" CssClass="form_submit"/>
</div>

So if I have a div with the class “form”, the default submit button is the first element with the “form_submit” class. Nice, simple and unobtrusive.

Here’s the javascript I ended up with:

$(document).ready(function(){
    var $btn = $('.form_submit');
    var $form = $btn.parents('.form');

    $form.keypress(function(e){
        if (e.which == 13 && e.target.type != 'textarea') {
            if ($btn[0].type == 'submit')
                $btn[0].click();
            else
                eval($btn[0].href);
            return false;
        }
    });
});

Basically it’s going to find any .form_submit elements, find a parent form, and add a keypress handler for the form. When the keypress is triggered, if it’s the enter key and we’re not in a textarea, we’ll click the default submit button if it IS a button, if it’s a link we’ll Eval the href attribute, which is going to be our javascript postback call.

Cool, I can keep it tucked away in an js file include, and i’ve improved my markup.

Tags: asp.net, javascript, jquery