11.4. Remote Call Parameters (The definitive guide of Symfony 1.2)

All the Ajax helpers described in the previous sections can take other parameters, in addition to the update and url parameters. The associative array of Ajax parameters can alter and tweak the behavior of the remote calls and the processing of their response.

11.4.1. Updating Distinct Elements According to the Response Status

If the remote action fails, the remote helpers can choose to update another element than the one updated by a successful response. To that purpose, just split the value of the update parameter into an associative array, and set different values for the element to update in cases of success and failure. This is of great use if, for instance, there are many Ajax interactions in a page and one error feedback zone. Listing 11-16 demonstrates handling a conditional update.

Listing 11-16 - Handling a Conditional Update

<div id="error"></div>
<div id="feedback"></div>
<p>Hello, World!</p>
<?php echo link_to_remote('Delete this post', array(
    'update'   => array('success' => 'feedback', 'failure' => 'error'),
    'url'      => 'post/delete?id='.$post->getId(),
)) ?>

Tip Only HTTP error codes (500, 404, and all codes not in the 2XX range) will trigger the failure update, not the actions returning sfView::ERROR. So if you want to make an action return an Ajax failure, it must call $this->getResponse()->setStatusCode(404) or similar.

11.4.2. Updating an Element According to Position

Just as with the update_element_function() helper, you can specify the element to update as relative to a specific element by adding a position parameter. Listing 11-17 shows an example.

Listing 11-17 - Using the Position Parameter to Change the Response Location

<div id="feedback"></div>
<p>Hello, World!</p>
<?php echo link_to_remote('Delete this post', array(
    'update'   => 'feedback',
    'url'      => 'post/delete?id='.$post->getId(),
    'position' => 'after',
)) ?>

This will insert the response of the Ajax call after the feedback element; that is, between the <div> and the <p>. With this method, you can do several Ajax calls and see the responses accumulate after the update element.

The position parameter can take the following values:

before: Before the element
after: After the element
top: At the top of the content of the element
bottom: At the bottom of the content of the element

11.4.3. Updating an Element According to a Condition

A remote call can take an additional parameter to allow confirmation by the user before actually submitting the XMLHttpRequest, as shown in Listing 11-18.

Listing 11-18 - Using the Confirm Parameter to Ask for a Confirmation Before Calling the Remote Function

<div id="feedback"></div>
<?php echo link_to_remote('Delete this post', array(
    'update'   => 'feedback',
    'url'      => 'post/delete?id='.$post->getId(),
    'confirm'  => 'Are you sure?',
)) ?>

A JavaScript dialog box showing "Are you sure?" will pop up when the user clicks the link, and the post/delete action will be called only if the user confirms his choice by clicking OK.

The remote call can also be conditioned by a test performed on the browser side (in JavaScript), if you provide a condition parameter, as shown in Listing 11-19.

Listing 11-19 - Conditionally Calling the Remote Function According to a Test on the Client Side

<div id="feedback"></div>
<?php echo link_to_remote('Delete this post', array(
    'update'    => 'feedback',
    'url'       => 'post/delete?id='.$post->getId(),
    'condition' => "$('elementID') == true",
)) ?>

11.4.4. Determining the Ajax Request Method

By default, Ajax requests are made with the POST method. If you want to make an Ajax call that doesn't modify data, or if you want to display a form that has built-in validation as the result of an Ajax call, you might need to change the Ajax request method to GET. The method option alters the Ajax request method, as shown in Listing 11-20.

Listing 11-20 - Changing the Ajax Request Method

<div id="feedback"></div>
<?php echo link_to_remote('Delete this post', array(
    'update'    => 'feedback',
    'url'       => 'post/delete?id='.$post->getId(),
    'method'    => 'get',
)) ?>

11.4.5. Authorizing Script Execution

If the response code of the Ajax call (the code sent by the server, inserted in the update element) contains JavaScript, you might be surprised to see that these scripts are not executed by default. This is to reduce remote attack risks and to allow script execution only when the developer knows for sure what code is in the response.

That's why you need to declare explicitly the ability to execute scripts in remote responses, with the script option. Listing 11-21 gives an example of an Ajax call declaring that JavaScript from the remote response can be executed.

Listing 11-21 - Authorizing Script Execution in the Ajax Response

<div id="feedback"></div>
<?php
  // If the response of the post/delete action contains JavaScript,
  // allow it to be executed by the browser
  echo link_to_remote('Delete this post', array(
    'update' => 'feedback',
    'url'    => 'post/delete?id='.$post->getId(),
    'script' => true,
)) ?>

If the remote template contains Ajax helpers (such as remote_function()), be aware that these PHP functions generate JavaScript code, and they won't execute unless you add the 'script' => true option.

Note Even if you enable script execution for the remote response, you won't actually see the scripts in the remote code, if you use a tool to check the generated code. The scripts will execute but will not appear in the code. Although peculiar, this behavior is perfectly normal.

11.4.6. Creating Callbacks

One important drawback of Ajax interactions is that they are invisible to the user until the zone to update is actually updated. This means that in cases of a slow network or server failure, users may believe that their action was taken into account, when it actually was not processed. This is why it is important to notify the user of the events of an Ajax interaction.

By default, each remote request is an asynchronous process during which various JavaScript callbacks can be triggered (for progress indicators and the like). All callbacks have access to the request object, which holds the underlying XMLHttpRequest. The callbacks correspond to the events of any Ajax interaction:

before: Before request is initiated
after: Immediately after request is initiated and before loading
loading: When the remote response is being loaded by the browser
loaded: When the browser has finished loading the remote response
interactive: When the user can interact with the remote response, even though it has not finished loading
success: When the XMLHttpRequest is completed, and the HTTP status code is in the 2XX range
failure: When the XMLHttpRequest is completed, and the HTTP status code is not in the 2XX range
404: When the request returns a 404 status
complete: When the XMLHttpRequest is complete (fires after success or failure, if they are present)

For instance, it is very common to show a loading indicator when a remote call is initiated, and to hide it once the response is received. To achieve that, simply add loading and complete parameters to the Ajax call, as shown in Listing 11-22.

Listing 11-22 - Using Ajax Callbacks to Show and Hide an Activity Indicator

<div id="feedback"></div>
<div id="indicator">Loading...</div>
<?php echo link_to_remote('Delete this post', array(
    'update'   => 'feedback',
    'url'      => 'post/delete?id='.$post->getId(),
    'loading'  => "Element.show('indicator')",
    'complete' => "Element.hide('indicator')",
)) ?>

The show and hide methods, as well as the JavaScript Element object, are other useful additions of Prototype.