US License Plate Spotter (part 2)

Last month I built a very basic mobile app using jQuery Mobile. It's still available here.

One flaw I found with jQuery Mobile is that it's a bit slow. Scrolling up and down feels sluggish. It looks pretty though.
This time around I opted instead to use Twitter Bootstrap instead. (inspired by some other blog post with a similar experience)

Also, with this version I've set up a domain name: uslicensespotter.com
The source code is available here and there are some interesting pieces of this that I'd like to delve into deeper.

Optimization

This new app feels faster and scrolling is smoother. There is still some parts where it doesn't feel snappy. The primary part is when you click one of the buttons. It works something like this:

// binding (simplified)
  $('form a.btn').click(function(event) {
    var $el = $(this);
    var id = $el.attr('id');
    if ($el.hasClass('btn-success')) {
      switch_off($el);
      State.remove(id);
    } else {
      switch_on($el, new Date());
      State.add(id);
    }
    return false;
  });


// the switch_on function
  function switch_on($el, timestamp) {
    $el.addClass('btn-success');
    $('i', $el).addClass('icon-white').removeClass('icon-remove').addClass('icon-check');
    $('span', $el).text(timeSince(timestamp));
  }

There are two potentials for making this faster.

1. Instead of using element.click(...) I can use touch events which supposedly fire better thus starting the actual animation earlier.
2. Instead of modifying the element (adding a class, adding a class, removing a class, adding a class, changing the text) what I could do is to remove the element from the DOM, manipulate it and then re-insert it back into the DOM. That way the (mobile) browser doesn't have to re-render after each manipulation.

My next task is to apply both of these ideas and try to somehow keep and eye on which makes the biggest impact.

Deployment

One neat new feature with this new code is the deployment script, build.py. The actual code might be a bit of a mess but the way it works for me is great.

What I do is that I work on the app by editing dev.html and when I deploy I run python build.py and it opens dev.html and concatenates and minifies all CSS and Javascript ready for ideal caching. This reduces the static assets down to just three files weighing only 78Kb altogether.

(Note: even more can be done such as switching to ZeptoJS and removing bootstrap stuff I don't need with a custom download)

What the script does is that it parses the dev.html template with lxml and applies whatever transformations it needs to do such as generating the Apple touch images eg. this one

I think a lot of mobile web developers can benefit from this script. Maybe you don't want to copy it verbatim but you might want to copy it and do the transformations you want to do.