Binding jQuery code to an XPages partialRefresh using DOM Mutation events

Introduction

In this article I will demonstrate how to bind to the event which triggers on the completion of an XPages partialRefresh. Using that binding we will then be able to action to contents of the newly added partialRefresh DOM elements.

Background

In multiple articles I have discussed the use of the onComplete event of a programmatically triggered partialRefresh to be able to re-apply a jQuery plugin’s bindings to an area of an XPage. This works very nicely and integrates with the Dojo events controlling the xhr request to the Domino server.

A problem arises when you do not have a programmatically controlled partialRefresh, say for example in a pager. XPages uses the same technology to execute a partial refresh on a viewPanel – but you and I do not have programmatic access to the onComplete event without hijacking it.

This was brought back to my attention when reading Brad Balassaitis’ excellent article on adding font awesome to his data view. In that case he does not have an event available to him through the XPages designer so he has to hijack the Dojo calls. A practical solution given the tools available.

In general though I have always found using the XPage events a non-elegant way of controlling the page and there has to be a better way – I think upon reflection this is a nice learning experience and “good to know” article but not practical in production.

DOM Mutation events

These events have been around for a whileย but are now “deprecated” in favor of the new MutationObserver() constructor which is unfortunately not implemented in Internet Explorer until IE11

  • DOMAttrModified
  • DOMAttributeNameChanged
  • DOMCharacterDataModified
  • DOMElementNameChanged
  • DOMNodeInserted
  • DOMNodeInsertedIntoDocument
  • DOMNodeRemoved
  • DOMNodeRemovedFromDocument
  • DOMSubtreeModified

As the mozilla article states – “The practical reasons to avoid the mutation events areย performance issues…...” – watching the DOM for changes every time a change happen has very processor intensive – believe me in my experiments if you latch onto DOMSubTreeModified and you are using jQuery which is constantly changing the DOM – you can easily drag your browser to its knees.

So in this article I am going to demonstrate how to use the “old” method for IE<11 and the preferred new method. You can then decide for yourself on the right way to do things – Dojo hijacking, degrading DOM performance or if you are lucky enough to not have to support IE – the way of the future ๐Ÿ™‚

An example of the general problem

If I have a simple view panel on a page and I use some jQuery to stripe the rows it looks pretty…..(yes there are other ways to stripe the rows this is just to demonstrate the point).

jq1

But as soon as I hit the pager – the striping is lost. The DOM elements are removed and the new elements do not have the striping applied

jq2

The partialRefresh

As I am sure most of you know the partialRefresh as genius as it is, works by POST-ing the field values on the form back to the server where the JSF licecycle processes these POST-ed values and then returns a new set of HTML to the browser. That new HTML is inserted as a direct replacement of the DOM element which was being refreshed. Looking at the response from the server you can see below that when paging through a viewPanel the viewPanel1_OUTER_TABLE is re-downloded from the server and replaces the existing Table element in the DOM.

jw3

So my striped table is deleted from the DOM and replaced – ergo no more striping.

DOM Node insertion

Using the DOM Mutation event DomNodeInserted it is actually relatively easy to re-stripe the table.

I first surrounded the viewPanel with a div wrapper “viewPanelWrapper”. This is what I will use to listen to changes for. Because the whole outer table is replaced I cannot listen to events on it – it is removed along with my binding.

The first piece of code will demonstrate the event listener

$('.viewPanelWrapper').on("DOMNodeInserted", function(){
    console.log('a node was inserted')
})

When I run the above code snippet through firebug you will see that nothing changes (1). But when I click Next the partialRefresh is triggered and “a node was inserted”
jq5

If we then take this a step further we can add in our striping code again

$('.viewPanelWrapper').on("DOMNodeInserted", function(){
    console.log('a node was inserted')
    $('.viewPanel TR:even').css({background: '#FFCCCC'})
})

And that’s pretty much it – pretty simple really.

jq6

So then extending this simple example you can see how a jQuery plugin could be reapplied to any page after a partialRefresh has been triggered – JUST BE AWARE THAT THERE IS A PRICE TO PAY IN PERFORMANCE. If you are going to do this then make sure that you pick the smallest area to check possible and that it does not change every second – your browsers and more importantly users will not thank you. On and applying a jQuery plugin almost certainly also modifies your DOM – be careful not to create an endless loop of pluging in your plugin.

So the “better way”

This article explains the reasoning behind the new MutationObserver and more importantly why it makes more sense than what I just showed you.

DOM MutationObserver โ€“ reacting to DOM changes without killing browser performance.

Check out the “So what are these good for” section at the end – obviously they were talking about XPages ๐Ÿ˜‰

Using a slightly modified version of their example we get this

var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver;
  var list = document.querySelector('.viewPanelWrapper');

  var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {

        console.log(mutation.type);
        $('.viewPanel TR:even').css({background: '#FFCCCC'})
    });
  });

  observer.observe(list, {
  	attributes: true,
  	childList: true,
  	characterData: true
   });

jq7

Which works the same but as the article explains – WAY more efficient and also gives you the control to not screw up your plugins.

Remember though the caveat is modern browsers and that it is IE11 only

Conclusion

Overall this has been a fascinating learning experience for me. I can’t recommend using the DOMNodeInserted event listener because it definitely caused me pain and anguish in browser performance. The MutationObserver is a very interesting concept but I am not convinced I would use it in an application until I better understand it.

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