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What is Flask-Webpack?

Managing assets can be a serious burden. Here's just a few things you get by using this package:

  • Minify assets
  • Attach vendor prefixes to your CSS automatically
  • Optimize image sizes
  • Leverage the CommonJS module system to organize your Javascript
  • Compile Markdown
  • Compile 20+ client side template languages
  • Compile LESS, SASS and any other CSS pre-processor you can imagine
  • Compile Typescript, Coffeescript and any other to-javascript language
  • Compile Ecmascript 6 (ES) down to ES 5
  • Compile React JSX to JS with hot module reloading
  • Near instant compile times, ~20-50ms is common on my workstation
  • Optionally get source maps in development mode
  • Serve your assets from a tricked out local development asset server
  • Cache all assets forever because their file names get md5-tagged
  • The only runtime you need other than Python is NodeJS
  • Never deal with file watchers again because it's all taken care of for you
  • And much more...

All of the features above are the direct result of using Webpack to manage your assets. The huge win here besides the obvious is that the functionality is outside of this package.

That means you have free reign to pick and choose what you want without having to worry about Flask-Webpack versions. If a new Webpack plugin becomes available, you can use it immediately.

What does this package do then?

It sets up a few template tags so you can access the assets inside of your jinja templates.

It means you can type this:

<img src="{{ asset_url_for('images/hamburger.svg') }}" alt="Hamburger">

...and once your jinja template has been compiled, you will see this:

<img src="images/hamburger.d2cb0dda3e8313b990e8dcf5e25d2d0f.svg" alt="Hamburger">

Now you can happily tell your frontend proxy to cache that hamburger image for an entire year. If you ever change the hamburger, the md5 will change but you do not need to change any of your templates because the asset_url_for tag knows how to look it up.

Global template tags

  • asset_url_for(asset_relative_path) to resolve an asset name
  • javascript_tag(*asset_relative_paths) to write out 1 or more script tags
  • stylesheet_tag(*asset_relative_paths) to write out 1 or more stylesheet tags

Both the javascript and stylesheet tags accept multiple arguments. If you give it more than argument it will create as many tags as needed.

Installation

pip install Flask-Webpack

Quick start

from flask import Flask
from flask_webpack import Webpack

webpack = Webpack()

app = Flask(__name__)
webpack.init_app(app)

You can view a complete working example in the test app.

There's also a blog post and short video explaining how to use this extension.

How does it work?

It expects you to have built a manifest file and it handles the rest. You can build this manifest file using a plugin I wrote for Webpack. You can find that plugin here.

This process is done automatically upon starting the dev asset server or building your assets to prepare for a production release. All of that is taken care of in the webpack.config.js file.

Settings

Flask-Webpack is configured like most Flask extensions. Here's the available options:

  • WEBPACK_MANIFEST_PATH: default None
    • Required: You may consider using ./build/manifest.json, it's up to you.
  • WEBPACK_ASSETS_URL: default publicPath from the webpack.config.js file
    • Optional: Use this asset url instead of the publicPath.
    • You would set this to your full domain name or CDN in production.

Learn more

Webpack knowledge

Most of what you'll need to learn is related to Webpack specifically but the example app in this repo is enough to get you started. Here's a few resources to help you get started with Webpack:

Help! My assets do not work outside of development

I see, so basically the problem is you're using the url() function in your stylesheets and are referencing a relative path to an asset, such as:

src: url('../../fonts/CoolFont.eot')

The above works in development mode because that's where the file is located but in production mode the asset is not there. The asset_url_for template helper handles all of this for you on the server side but now you need some assistance on the client side as well.

You have a few options here depending on if you're using CSS, SASS or something else. If you're using straight CSS you will need to pre-prend all of your paths with a special identifier.

If you were to re-write the example from above, it would now be:

src: url('~!file!../../fonts/CoolFont.eot')

That will automatically get expanded to a path that works in every environment.

If you're using SASS you can create your own function to make things easier to work with on a day to day basis. Something like this should suffice:

@function asset-url($path) {
  @return url('~!file!' + $path);
}

Now you can call it like this and everything will work:

src: asset-url('../../fonts/CoolFont.eot')

Feel free to make additional helper functions that let you abstract away the relative prefix such as font-url or image-url. It really depends on how your assets are set up.

Contributors