Posts tagged JavaScript

AJAX performance boosts

28 Jan 2011
by in BibGrab, CLUMP, LORLS

Just recently I have been looking at tweaks that I can make to improve the performance of CLUMP.  Here are the ones that I have found make a difference.

Set up apache to use gzip to compress things before passing them to the browser.  It doesn’t make much difference on the smaller XML results being, but on the large chunks of XML being returned it reduces the size quite a lot.

Here is an extract of the apache configuration file that we use to compress text, html, javascript, css and xml files before sending them.

# compress text, html, javascript, css, xml:
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript

Another thing is if you have a lot of outstanding AJAX requests queued up and the user clicks on something which results in those requests no longer being relevant then the browser will still process those requests. Cancelling them will free up the browser to get straight on with the new AJAX requests.

This can be very important on versions 7 and below of Internet Explorer which only allow 2 concurrent connections to a server over http1.1. If the unneeded AJAX requests aren’t cancelled and just left to complete then it can take Internet Explorer a while to clear the queue out only processing 2 requests at a time.

The good news is that Internet Explorer 8 increases the concurrent number of connections to 6, assuming that you have at least a broadband connection speed, which brings it back into align with most other browsers.

‘Copy To’ Added to CLUMP

10 Jun 2010
by in CLUMP, LORLS

I have now added the ‘Copy To’ functionality to CLUMP. It presents a list of the owners reading lists to them with checkboxes and they can select which ones they want to copy the item to. Once they have chosen the lists to copy the item to they click ‘copy’ and it calls LUMP’s CopySU API to copy the structural unit to each reading list selected.

Because the CopySU API can take a while to run at the minute I use the asynchronous aspect of JavaScript to make all the CopySU calls without waiting for the previous one to complete.  This lead to the problem of “how do I wait till all the calls have completed?”.  There is no “wait till all my callbacks have run” option in JavaScript so I ended up having to increment a counter for each call and then have the callback function decrement the counter.  If the counter reaches 0 then the callback function runs the code that we need to run after all of the CopySU API calls have completed (In this case close the popups and reload the current structural unit if it was one of the targets).

Another Debugging Tip

14 Jan 2010
by in CLUMP, LORLS

As we reach the stage where we will be demoing LORLS v6 more often I figured it was time to make my debugging code easy to switch off.  This resulted in two new JavaScript functions debug and debugWarn.  They both are wrappers that first check the global variable DEBUG and if it is set then they call the relevant method from the console object (either log or warn).

Now to switch of debug messages we simple set DEBUG to 0 and to switch them back on we set it to 1.

How Best To Debug JavaScript.

01 Oct 2009
by in CLUMP, LORLS

While starting to look at creating an AJAX client for LUMP I have come up against the old problem of how best to debug the code.  Depending on the browser being used it debugging can be very easy or very difficult.  FireFox, Google Chrome, etc. all give access to JavaScript consoles either natively or via a plug-in like FireBug.  The problem comes with Internet Explorer (IE) that is very weak in the debuging side of things.

There is FireBug Lite which is a cut down version of FireBug that you can add into the web page HTML, the problem with this is that also then appears on your other browsers and sometimes seems to cause problems with them.  I don’t want to have code in my client that say if you have this browser then do this and if you have that browser do that as it makes it difficult the maintain.

The solution that I am using is the following bit of code at the start

if(typeof(console)=='undefined')
{
  console={
    log: function (x) {alert(x);},
    warn: function (x) {alert(x);}
  };
}

Quite simply it looks to see if there is a console object available and if not it creates a simple one which supports log and warn, the two debugging statements that I use most.  If there isn’t a console to log to all log and warn messages will appear as alerts to the user.  This can be annoying in IE but it is usually only IE specific problems that I am trying to debug in IE.

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