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декември 11, 2013

Component goodness (Polymer) - (with update on readiness)

After several months of active development I think Polymer deserves another trial / deep look.

My initial reactions to it was negative due to several assumptions I had:
  • there is no way to compile down to one file
  • there is no 'global compile-time checking'
It seems my first objection is now being addressed and there will be a way to compile down all the imports and links into one single file, which is great. The second one is hard to explain if you are not used to Dart or Closure ways of doing things, but basically they make compile time graph of all your calls and compile an AST of your application and operate on it (checks, asserts, rewrites etc). The thing is that you should not really need that if you use the declarative approach to build your application, which is what Polymer assumes you are trying to do.

So how do we do this?

First go get the code. I used c9.io workspace, but if you have a Linux/MacOSX machine you can do this locally. I tried all the methods: zip archive, git pull and bower - all of them work, but some of the examples need path tweaking to find the files. Also you might need to add both polymer.js and platform.js if non-minified version is used (bower and git).

I find that one of the most interesting tests one can do with a new technology is to try and build something complex that you have already built with another technology. Then compare the result, the experience and the speed of development between the two approaches.

My intent is to use Longa as a product developed with Closure tools and to try to re-create it with Polymer.

Longa is a large product (~2MB unprocessed JS and templates). Compiled with closure compiler it is boiled down to 115KB (JS plus the templates) and is further compressed by the server to 30KB, which makes a reasonable download size for a mobile web application. 

The HTML cannot be compiled down (names matter, its not like JavaScript), thus the savings should be coming from a more compact expression forms. 

For now I have re-created only a single channel record and I could say I am already impressed with what the platform is capable of doing without actually me needing to write any code at all. Of course there is much to be done and even more to be desired.

For example the styling of two shadowed elements do not work as I was expecting (in the context of a single polymer element and the elements are regular ones - a div and an image tag). Maybe it is a bug, maybe I am missing something, but still it is kind of a hurdle for a new comer, regardless of how many tutorials are out there, pretty much all of them concentrate their efforts on the area of isolating the styles from the outside world and not on how they work internally.

One of the most interesting things I notices was the fact that you can bind the styling of an element and mix it with an expression, so an element can calculate style values based on properties and arithmetics. For example:

#selector { height: {{height+20}}px; }

is a valid style inside the template of an element!

Another interesting factor is the abstraction of complex routines into elements. For example ajax calls are hidden in an element and you can listen on that element or any of its parents and use it as a regular element (just like the select or change events in native controls).

All in all it is at least an interesting toy. I am not sure how fast the browsers will get to the point where all this will work without hacks or shims, but at least for a certain class of applications it will be a nice fresh breath out of the JS insanity we have been living with for the last 10 years. 

As a conclusion: even if your code is very complex (for example something like a drawing board or document viewer) you can at least try and ship it as a web component so others can use it in the simplest form possible, by just import it and use it as a tag in their markup. I for one will try that!

Update (12/16/2013): Turns out most of the things do not work in FF/Mobile Safari, especially the styling. Some style rules do not work in Chrome even with no apparent reason. For example rule like this:

padding-left: 4px;

does not work but this one does:

padding: 0 0 0 4px;

I guess there are still lots of bugs and features missing, but clearly if you want to just tap your fingers into the power of the web components now is a suitable time. However if you want to go to full blown large apps you should definitely wait at least a few months! 

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