Integrate Scala.js into the XForms/Form Runner client

[ebruchez]

We crave using Scala on the client!

• Scala.js is no longer experimental as of early 2015.
• impact on JS size
  • uncompressed optimized JS for small project w/ e.g. Vector and List: ~200-300 KB
  • compressed: ~70 KB
  • would add ~100 KB for moderate code size on the client
  • could offset some of this by removing some legacy libraries (see Progressively get rid of YUI #1599, Remove YUI RTE and map HTML textarea to tinyMCE #1249, etc.)
• impact on development
  • right now compiled w/ sbt
  • reloads in browser not as instant as with JS/CoffeeScript
  • roundtrip for very small project ~5 seconds to reload w/ Chrome dev tools
• impact on build system
  • need to figure that out, but build system needs modernization anyway

[ebruchez]

The current thinking is to start with Form Builder, which:

• requires more complex client-side code
• has higher browser requirements
• is often installed in controlled environments

Therefore, adding JavaScript code shouldn't be an issue.

Candidate features to investigate:

• Ability to move controls with drag and drop Ability to move controls with drag and drop #1479

[avernet]

I'm tempted to schedule making some progress on this for 4.8, if only because working on this is pretty exciting. (Is that a good or a bad excuse?)

[ebruchez]

Update to the "current thinking" above: the admin console could also be a candidate.

[ebruchez]

Some numbers as of 4.9:

• baseline JS:
  • 221 KB of compressed optimized JS (913 KB non-compressed)
• Controls form additional JS:
  • 111 KB compressed (348 KB uncompressed)
  • total 332 KB compressed
• Form Builder additional JS:
  • 180 KB compressed (635 KB uncompressed)
  • total 401 KB compressed

[ebruchez]

As an update, there will be quite a lot of Scala.js in Form Builder (but not Form Runner) in the next version. We'll see what the impact on JavaScript size is, as a new data point.

[ebruchez]

Above comment is quite outdated as the Form Builder UI for the workflow feature got written in XForms.

Currently, orbeon-form-builder-client-opt.js:

• includes some immutable collections like Vector and List
• weighs 140 KB uncompressed
• weighs 36 KB compressed!

Things have progressed nicely since March 2014, with files about 1/2 the size (although we are not comparing exactly the same things but hopefully we are not too far off).

Still, it would be good not to duplicate the JavaScript between Form Runner and Form Builder if possible, although that would only impact Form Builder.

Doing this would require something like this:

• formBuilder project produces its own fastopt
• formRunner project produces its own fastopt
• root project (or other) links and produces opt output

Now thinking that the above only makes sense if the additional weight of Form Builder code is very small compared to the rest of the Form Runner code.

So maybe something better, until some kind of code-splitting feature makes it to Scala.js, would be:

• Form Runner has its own code in a single JavaScript file
• Form Builder has also a single JavaScript file but which is the result of compiling the Form Builder + the Form Runner code

[ebruchez]

For 2017.1, do baby steps:

• setup build to include Scala.js for core (XForms, actually) and/or formRunner
  • follow or revisit if needed decision above on Form Builder/Form Runner split
• make fr:dnd-repeat part of Form Runner
• fix Summary page loads Form Builder JavaScript #3090
• move FormRunnerApp from formRunnerComponents to core or XForms or formRunner