Set - 3

Question 6 :

How do I submit a form or a part of a form without a page refresh?

Answer :

When creating a form make sure that the "form" element "onSubmit" attribute is set to a JavaScript function that returns false.

<form onSubmit="doAJAXSubmit();return false;" >
<input type="text" id="tf1" />
<input type="submit" id="submit1" value="Update"/>
</form>

You can also submit data by associating a function with a form button in a similar way.

<form onSubmit="doAJAXSubmit();return false;" >
<input type="text" id="tf1" />
<input type="button" id="button1" onClick="doAJAXSubmit()" value="Update"/>
</form>

Note that the form "onSubmit" attribute is still set. If the user hits the enter key in the text field the form will be submitted so you still need to handle that case.
When updating the page it is recommend you wait to make sure that the AJAX update of the form data was successful before updating the data in the page. Otherwise, the data may not properly update and the user may not know. I like to provide an informative message when doing a partial update and upon a successful AJAX interaction I will then update the page.


Question 7 :

How do I get the XMLHttpRequest object?

Answer :

Depending upon the browser...

if (window.ActiveXObject) { // Internet Explorer http_request = new ActiveXObject("Microsoft.XMLHTTP"); } else if...


Question 8 :

How do I handle the back and forward buttons?

Answer :

While you could go out and create a custom solution that tracks the current state on your application I recommend you leave this to the experts. Dojo addresses the navigation in a browser neutral way as can be seen in the JavaScript example below. 

function updateOnServer(oldId, oldValue, 
    itemId, itemValue) {
    var bindArgs = {
    url: "faces/ajax-dlabel-update",
    method: "post",
    content: {"component-id": itemId, "component-value":
    itemValue},
    mimetype: "text/xml",
    load: function(type, data) {
    processUpdateResponse(data);
    },
    backButton: function() {
    alert("old itemid was " + oldId);
    },
    forwardButton: function(){
    alert("forward we must go!");
    }
    };
    dojo.io.bind(bindArgs);
}

The example above will update a value on the server using dojo.io.bind() with a function as a property that is responsible for dealing with the browser back button event. As a developer you are capable of restoring the value to the oldValue or taking any other action that you see fit. The underlying details of how the how the browser button event are detected are hidden from the developer by Dojo. 
AJAX: How to Handle Bookmarks and Back Buttons details this problem and provides a JavaScript library Really Simple History framework (RSH) that focuses just on the back and forward issue.


Question 9 :

How do I send an image using AJAX?

Answer :

While it may appear that images are being sent when using AJAX with an application like Google Maps what is really happening is that the URLs of images are being send as the response of an AJAX request and those URLs are being set using DHTML. 
In this example an XML document is returned from an AJAX interaction and the category bar is populated.

<categories>
<category>
<cat-id>1</cat-id>
<name>Books</name>
<description>Fun to read</description>
<image-url>books_icon.gif</image-url>
</category>
<category>
<cat-id>2</cat-id>
<name>Electronics</name>
<description>Must have gadgets</description>
<image-url>electronics.gif</image-url>
</category>
</categories>

Notice that the image-url element contains the location of the URL for the image representing a category. The callback method of an AJAX interaction will parse the response XML document and call the addCategory function for each category included in the response XML document. The addCategory function looks up a table row element "categoryTable" in body of the page and adds a row to the element which contains the image.

<scrip type="text/javascript" >
function addCategory(id, name, imageSrc) {

var categoryTable = document.getElementById("categoryTable");
var row = document.createElement("tr");
var catCell = document.createElement("td");
var img = document.createElement("img");
img.src = ("images\\" + imageSrc);
var link = document.createElement("a");
link.className ="category";
link.appendChild(document.createTextNode(name));
link.setAttribute("onclick", "catalog?command=category&catid=" + id);
catCell.appendChild(img);
catCell.appendChild(link);
row.appendChild(catCell);
categoryTable.appendChild(row);
}
</script>
<table>
<tr>
<td width="300" bgoclor="lightGray">
<table id="categoryTable" border="0" cellpadding="0"></table>
</td>
<td id="body" width="100%">Body Here</td>
</tr>
</table>

Note that the source of the image is set to the image source. The image is loaded by a subsequent HTTP request for the image at the URL "images/books_icon.gif" or "images/electronic_icon.gif" that occurs when the img element is added to the categoryTable.


Question 10 :

Will HTML_AJAX integrate with other Javascript AJAX libraries such as scriptaculous ? How would this integration look like?

Answer :

HTML_AJAX doesn't have specific plans to integrate with other JavaScript libraries. Part of this is because external dependencies make for a more complicated installation process. It might make sense to offer some optional dependencies on a library like scriptaculous automatically using its visual effects for the loading box or something, but there isn't a lot to gain from making default visuals like that flashier since they are designed to be easily replaceable.

Most integration would take place in higher level components. Its unclear whether higher level components like that should be part of HTML_AJAX delivered through PEAR or if they should just be supported by HTML_AJAX and made available from http://htmlajax.org or some other site. If your interested in building widgets or components based on HTML_AJAX please let me know.

HTML_AJAX does however offer the ability to use its library loading mechanism with any JavaScript library. I use scriptaculous in conjunction with HTML_AJAX and I load both libraries through the server.

To do this you just need to register the library with your server and load add its flag to your include line.

$this->server->registerJSLibrary('scriptaculous',
array('prototype.js','scriptaculous.js','builder.js','effects.js','dragdrop.js','controls.js','slider.js'), '/pathto/scriptaculous/');
<script type="text/javascrpt" src="server.php?client=scriptaculous"></script>