Author: mattsouth

I took a reasonably deep dive into JsonLogic recently, evaluating it as a possible drop-in replacement for expression evaluation in proformajs. In the process I got my hands dirty with vue3 and bootstrap5 to create a JsonLogic sandbox along with a library for serialising JsonLogic expressions that maybe useful.

The library is indeed a suitable drop-in but the evaluation process has made me think twice of leveraging javascript expression semantics. Though it was a prudent time saving strategy at the time it was made, it may need reviewing.

My family spent a week in Finland this summer as part of our summer holiday. One of the many highlights was a visit to the design museum in Helsinki which is excellent and well worth a visit if you go there. The ground floor was dedicated to the work of Margrethe Odgaard, an artist/artisan from Copenhagen who has an exquisite eye for colour, particularly, but not exclusively, in textiles. One of the things presented were colour diaries that she’d kept on visits to Morocco and Cuba that were fascinating and beautiful. It gave me an idea for a simple phone app that I could build that would allow me to do the same thing, so I created it using Meteor. If you have an android phone, you can download it for yourself from the Google Play store. It’s in beta because Ive not done this before and at the moment I only know that it works on my phone. I’d love to hear any feedback you might have.

Coffeescript has a nice way of destructuring assignment in a class constructor, e.g.

class Person
  constructor: (options) ->
    {@name, @age, @height} = options

This is elegant and efficient and has the additional benefit of explicitly communicating anticipated class attributes, cf:

class Person
  constructor: (options={}) ->
    for key, val of options
      @[key] = val

which allows any old thing to be added to your object (although admittedly this is sometimes desirable).

Coffeescript also has a neat way of setting default values for functions, e.g.

fill = (container, liquid = "coffee") ->
  "Filling the #{container} with #{liquid}..."

But this pattern doesnt seem to transfer to destructuring class assignment.  I can’t for instance use any of these approaches:

class Person
  constructor: (options) ->
    {@name = "Ken", @age, @height} = options # (yields an "UNEXPECTED=" error) or
    {@name: "Ken", @age, @height} = options # (yields a "Ken" CANNOT BE ASSIGNED error)
    {@name ?= "Ken", @age, @height} = options # (yields an "UNEXPECTED COMPOUND ASSIGN" error)
    {@name? "Ken", @age, @height} = options # (yields an "UNEXPECTED LOGIC" error)
    {@name || "Ken", @age, @height} = options # (yields an "UNEXPECTED LOGIC" error)

It turns out that the best way (IMO) is:

class Person
  constructor: (options={}) ->
    {@age, @height} = options;
    @name = options.name ? "Ken"

Note that the default value for options is included, so as not to force a parameter on the constructor.  As always, stack overflow provides a deeper picture.

Last year in a slow period I knocked up a javascript library for making wooden toy train designs as a useful/interesting exercise.  After getting some implicit feedback on it last week (somewhat baffled), I decided to review it, give it a spruce up and add some more explanation.  It’s still barely a proof of concept but you can see the results here.

The next pieces of work (should I get the chance) will probably focus on:

1. finessing the API, i.e.   “Create a track at the browser command prompt, attach a track painter and watch the drawn track change as you add/remove pieces and edit the track properties” and
2. adding annotations to the free ends of track drawn in the DSL demo so it’s clear how to add more track to them.