JavaScript and Python back-endMax Klymyshyn

oDesk PS

Twitter: @maxmaxmaxmaxGithub: joymax

Sources:goo.gl/zbtXH

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The problem

JavaScript code grew up on the Project

Optimization of the Application become the pain in the ass

Hard to manage dependencies and test updates

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The solution

Add Assets Management tools to the project

Define and follow conventions

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TOCProject Structure

Assets management

JavaScript Templates

Constants within JS files

Browser-specific assets

SCSS/LESS

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Note

This presentation based on Flask but it's possible to use Django or any other framework which supported by Webassets

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Project structure• app.py• assets.py

• templates• base.html

• bundles• browsers.py• jstemplates.py• scss_bundle.py• vars.py

• static• src

• js• css

• js• css

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Assets management

core = Bundle( "src/js/lib/core/*.js", "src/js/lib/*.js", output="core.js")

assets.register("js_core", core)

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JavaScript Templates var %(namespace)s = %(namespace)s || {}; %(namespace)s._assign = function (obj, keyPath, value) { var lastKeyIndex = keyPath.length - 1; for (var i = 0; i < lastKeyIndex; i++) { key = keyPath[i]; if (typeof obj[key] === "undefined") { obj[key] = {}; } obj = obj[key]; } obj[keyPath[lastKeyIndex]] = value; }; (function(){

// ... here should be templates definitions})();

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JavaScript templates

templates = ( 'system/*.tpl', 'views/main/*.tpl', 'views/group/*.tpl', 'views/rate/*.tpl', 'views/search/*.tpl', 'views/sort/*.tpl', 'views/progress/*.tpl', 'views/sidebar/listings/*.tpl', 'views/sidebar/search/*.tpl', )

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Constants within JavaScript def constants(app): cfg = {} with app.test_request_context(): cfg.update(dict( API_URL=url_for("api", _external=True), TITLE="Sample Widget" )) return cfg

conf_app = JSVarsBundle("src/js/conf/main.js", output="js/compiled/conf/conf.js", vars=constants(app), filters=[“yui_js”], ignore_filters=assets.debug)

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Constants within JavaScript Configuration file looks like:

...

_.defaults(config, { 'api_url': '$$API_URL', 'title': '$$TITLE' });

window.KHARKIVPY.config = config;

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Browser-specific assets

We need to load custom assets for different browsers

We don’t have ability to use conditional commends for IEs (business requirement)

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Browser-specific assets chrome17 = BrowserBundle( 'src/css/browsers/chrome17.css', browser='Chrome', browser_version='17', output='css/chrome17.css' )... browserspec_assets_loader = LoaderBrowserBundle( 'src/css/browsers/safari5.css', # dirty hack, we’ll change it bundles=[chrome17, safari5], filters='loader_browser', output='js/compiled/assets-loader.js' )

assets.register("browserspec_assets_loader",browserspec_assets_loader)

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Browser-specific assetsBelow is generated snippet by webassets bundle:

(function (assets) { BrowserAssets('/static/', assets);})({'Chrome': {

'17': ['src/css/browsers/chrome17.css']}, 'Safari': {

'5.1': ['src/css/browsers/safari5.css']}});

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SCSS/LESS

It was painful to maintain raw CSS for complex public widget

We declined to use LESS because we aren’t found good and maintainable LESS compiler for Python

We decided to not use client-side LESS parser to avoid possible conflicts with client’s code

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SCSS/LESSstyle_files = ( 'reset.scss', 'base.scss',)

register_scss_bundle( style_files, assets=assets, name='css_core', output='css/style.css', prefix='src/css', compile_to='css/compiled')

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CDN (Amazon CloudFront)

Sometimes back-end server goes down

Clients and partners may experience really weird behavior and look of the Widget when back-end not available

No one want to loose face in front of the client

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CDN (Amazon CloudFront)

All of static related to the Widget hosted on Amazon CloudFront

In case back-end goes down for maintenance or because of failure JavaScript display nice error

Widget still looks like it should

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CDN Pitfalls

Amazon CloudFront may update your files REALLY SLOW

It may take up to 24 hrs to spread updates to all CDN nodes around the world

You may experience hard time with your product owner

CDN is for really patient clients

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Questions?

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