LTD 404

Error page for LSST the Docs, served at the edge by the Fastly CDN.

This page is shown by the Fastly CDN when a user requests a page that doesn't exist on the backend (S3).

Getting started with development

Get the repo:

git clone https://github.com/lsst-sqre/ltd-404
cd ltd-404

Install JavaScript dependencies:

npm install -g gulp-cli
npm install

Compile the page and start a development server with Browsersync:

gulp

This default Gulp task watches for changes to the HTML, CSS, and JavaScript, recompiles the page, and reloads the browser as necessary. You'll want to leave a terminal running this Gulp task while you develop the site to see you changes rendered live.

When you're ready to deploy, follow the steps in deployment.

Codebase orientation

There are three files you'll edit to make 404 page:

404.html. This is rendered into _build/404.html, with all CSS and JavaScript inlined.
styles.scss. This Sass file is rendered into styles.css.
app.js. The JavaScript is developed in ES6, and compiled into ES5 as the file app.bundle.js. The role of this JavaScript is primarily to look at the current URL (using the location API) and suggest other URLs lower down in the tree (like the site's homepage, or the /v/ version dashboard of LSST the Docs sites).

Gulp commands

This project uses Gulp to run its build pipelines. This section describes the gulp commands you can run.

gulp

Use this default command for development. It does the following:

js (compile JavaScript)
sass (compile Sass)
watch (run Browsersync and reload whenever the files change)

gulp build

Compile the fully-packaged 404 page for deployment on Fastly. See: deployment.

gulp sass

Compile Sass into CSS (styles.css). We use the following features

Compile Sass.
Add prefixes to CSS using Autoprefixer (via PostCSS).
Clean and compress the CSS using gulp-clean-css.

You can run this task alone, but usually through either gulp or gulp build.

gulp js

Packages the JavaScript with Webpack into app.bundle.js. Most importantly, Webpack runs Babel to compile the ES6 JavaScript into ES5 that most browsers can run. The webpack.config.js describes how Webpack and Babel are set up.

You can run this task alone, but usually through either gulp or gulp build.

gulp html

This task creates the production-ready HTML by inlining all assets into the page. It uses gulp-inline-source to do this.

Normally you'll never run this task on its own, but instead through gulp build. Inlining isn't part of the development working with the default gulp command.

gulp watch

This command does two things:

Starts up Browsersync to server your page locally and to trigger page reloads.
Watches for changes to HTML, JavaScript, and CSS and triggers a recompile and browser reload.

Normally you'll only run this command via the default gulp task.

By default, Browsersync serves your page at https://localhost:3000/.

gulp pretty

Automatically format code. See Code style via Prettier.

gulp lint

Lint the code for errors and style. See Code linting via ESLint.

Deployment

You need to install the 404 page directly on the Fastly CDN. It isn't deployed from AWS S3 like most LSST the Docs front-end content.

Build the page for production:
```
gulp build
```
The output is in _build/404.html.

Log into the lsst-the-docs service page on Fastly.
Clone the current configuration.
Copy the _build/404.html page's content and paste it into the 404 Response response (under Content → Responses).
Activate the new configuration.

Background: Creating error pages with custom responses (Fastly docs).

Note: Avoid minifying 404.html. It turns out Webpack's production minification can trip up the VCL in Fastly.

Code style via Prettier

This project uses Prettier to make sure the Sass and JavaScript are formatted as you'd expect. Like most projects, we use Prettier nearly as-is. A couple minor exceptions are configured in .prettierrc.yaml.

You can run Prettier two ways:

Manually, by running gulp pretty.
Automatically, by committing code. This is configured as a pre-commit hook in package.json.

Note that Prettier's pre-commit hook and chunked git commits don't mix. You'll want to manually run Prettier before committing a subset of the changed lines in your files.

Code linting via ESLint

We use ESLint as a first line of defense for JavaScript code quality. You can run ESLint via:

gulp lint

Linting is also done via Travis CI (see .travis.yml).

ESLint is configured through .eslintrc.json.

License

LTD 404 is open source software made by the Large Synoptic Survey Telescope. See the included LICENSE file for details.