Custom Elements
billstclair/elm-custom-element is a package to collect Html custom element implementations.
Note that when you use the included modules in your project, they won't actually DO anything unless you follow the instructions below to load their JavaScript files.
Here are the custom element modules:
-
CustomElement.TextAreaTrackerAttach a
<text-area-tracker>to a<textarea>or<input type='text'>element. When triggered, it sends events from which you may extract the current selection start and end and the screen coordinates of the insertion cursor. This enables popping up a completion dialog for, e.g., completing@foonicknames. -
CustomElement.FileListenerAttach a
<file-listener>to a<file>element, and when the user chooses a file, you'll get an event containing the file's content as both a string and a Data URL.JavaScript file:
site/js/file-listener.jsThis was a kludge to enable uploading binary files before
elm/httpv2.x,elm/file, andelm/bytes. If you still need to useelm/http1.x, then using this makes sense. For new code, useelm/filewithelm/httpv2.x. -
CustomElement.CodeEditorA simple wrapper around the CodeMirror code editor. Inspired by Luke Westby's Elm Europe talk.
JavaScript file:
site/js/code-editor.jsSupport files:site/lib/ codemirror.css, codemirror.js
Adding Custom Elements to Your Project
In order to use custom elements, you must start your project from a .html that includes your compiled Elm file and the custom element JavaScript files, and any port code you need. You can start this by copying the site directory from here to your project, then edit site/index.html. Remove the custom elements you don't need from its <head> section, and customize anything else that needs it. Only include in your application the files in the site/js directory for custom elements you use.
$ git clone git@github.com:billstclair/elm-custom-element.git
$ cd elm-custom-element
$ cp -R site .../<your project directory>/
$ cd .../<your project directory>
$ <editor> index.html
The included index.html assumes your Elm code is in elm.js. You can make this so with something like the following:
elm make src/Main.elm --output site/elm.js
I usually run my Elm projects during development using elm reactor, if only beacause some browsers aren't happy with file: URLs:
$ cd .../<project-dir>
$ elm reactor
Then aim your browser at http://localhost:8000/site/index.html
Building and Running the Example
The file src/Main.elm is an example of using the included custom elements.
To build and run it:
$ git clone git@github.com:billstclair/elm-custom-element.git
$ cd elm-custom-element
$ elm make src/Main.elm --output site/elm.js
$ elm reactor
Then aim your web browser at http://localhost:8000/site/index.html
The example is live at billstclair.github.io/elm-custom-element
Help to Expand the Library
I encourage pull requests, for custom elements that you think will be useful to the community. To add a custom element, do the following:
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Fork billstclair/elm-custom-element on GitHub.
-
Add your JavaScript file to the
site/jsdirectory. The file should be patterned afterfile-listener.js, defining NO top-level variables or functions. Add a<script>element tosite/index.htmlto load your JavaScript file. -
If your custom element requires JavaScript written by somebody else, put those files in the
site/libdirectory, and editsite/lib/README.mdto include a description of those files and their license(s). Add<script>elements tosite/index.htmlfor those files, too. -
Add your Elm interface file to the
src/CustomElementdirectory. The file should be patterned afterFileListener.elm, exposing a function to create your custom element(s), one of more functions returning anHtml.Attributeto set properties of the element, one or more functions returning anHtml.Attributeto handle an event from the element, and any convenience functions that make sense. -
Add your new module to the
exposed-modulesinelm.json. -
Add an example of using your element to
example/Main.elm, expanding itsModelandMsgas necessary, and adding display code toviewand event handling code toupdate. -
Test your example, using the instructions above.
-
Add your element to the list above in this
README.mdfile. -
Ensure your exposed interface is all documented with:
elm make --docs docs.json -
Review
README.mdanddocs.jsonwith https://elm-doc-preview.netlify.com -
Submit a pull request. Don't worry about bumping the version number. I'll do that.
Compatibility
The Custom Elements Registry is still a fairly new part of the web browser DOM. It isn't supported by all browsers, as outlined in the compatibility table on that page.
In particular, Microsoft Internet Explorer and Edge do not support custom elements. There's a polyfill, and I included that in site/lib/custom-elements.min.js, but it didn't make the example work in IE on my Windows machine, though it DID make it work in Firefox on my Mac desktop, without setting dom.webcomponents.customelements.enabled true in about:config (the polyfill isn't necessary, if you do that). I commented out the inclusion of the polyfill in site/index.html. Use it if you wish.
If you're motivated to make the code work for IE and/or Edge, or for other browsers that don't currently work, I'll gladly accept a pull request that does that.
Bill St. Clair, 9 October 2018
