Prior to doing a code review for this sim we should make sure we tick all the check boxes

PhET code-review checklist

Build and Run Checks

[x] Does the sim pass lint?
[x] Does the sim start up? (requirejs and built versions)
[x] Does the sim experience any assertion failures? (run with query parameter 'ea')
[x] Does the sim pass a scenery fuzzer test? (run with query parameter 'fuzzMouse')

Strings

[x] Are there any unused strings? (Strings that appear in the JSON file but are unused in the simulation should be removed).
[x] Are there any strings that are not being internationalized? (run with query parameter 'stringTest=x', you should see nothing but 'x' strings)
[x] Does the sim layout gracefully handle internationalized strings that are twice as long as the English strings? (run with query parameter 'stringTest=double')
[x] Does the sim layout gracefully handle internationalized strings that are exceptionally long? (run with query parameter 'stringTest=long')
[x] Does the sim stay on the sim page (doesn't redirect to an external page) when running with the query parameter 'stringTest=xss'. Only test on one desktop platform.
[x] Does the sim layout gracefully handle internationalized strings that are shorter than the English strings? (run with query parameter 'stringTest=X')
[x] Make sure the string keys are all perfect, they are difficult to change after 1.0.0 published.

Repository structure

[x] Are all required files and directories present?

For a sim repository named “my-repo”, the general structure should look like this (where assets/, audio/ or images/ may be omitted if the sim doesn’t have those types of assets).

   my-repo/
      assets/
      audio/
         license.json
      doc/
         model.md
         implementation-notes.md
      images/
         license.json
      js/
         my-repo-config.js
         my-repo-main.js
      .gitignore
      my-repo_en.html
      my-repo-strings_en.json
      Gruntfile.js
      LICENSE
      package.json
      README.md

For a common-code repository, the structure is similar, but some of the files and directories may not be present if the repo doesn’t have audio, images, strings, or a demo application.

[x] Is the js/ directory properly structured?

All JavaScript source should be in the js/ directory. There should be a subdirectory for each screen (this also applies for single-screen sims). For a multi-screen sim, code shared by 2 or more screens should be in a js/common/ subdirectory. Model and view code should be in model/ and view/ subdirectories for each screen and common/. For example, for a sim with screens “Introduction” and “Custom”, the general directory structure should look like this:

   my-repo/
      js/
         common/
            model/
            view/
         custom
            model/
            view/
         introduction
            model/
            view/
         my-repo-config.js
         my-repo-main.js

[x] Is there a file in assets/ for every file in audio/ and images/?
[x] Are all license.json files populated? audio/license.json and images/license.json should enumerate all files in those directories. For the format of license.json files, go here.
[x] Does the README.md format and content match PhET guidelines? Was it generated by grunt published-README or grunt unpublished-README?
[x] Does Gruntfile.js point to chipper/js/grunt/Gruntfile.js?
[x] Are dependencies in package.json the same as js/*-config.js? Do they match what is actually used by the sim? (ie, no missing dependencies, no unused dependencies)
[x] Is the LICENSE file correct? (Generally GPL v3 for sims, MIT for common code, but there are exceptions to this.)
[x] Does .gitignore match other repositories?
[x] Does *-main.js follow PhET conventions? Does it contain correct credits (options.credits passed to Sim constructor)?
[ ] Are there git repository branches that are no longer used and should be pruned?

Coding conventions

[x] Does the code style meet PhET's code-style guidelines, as described in the “Coding Style Guidelines” section of "PhET Development Overview"?
[x] Is the code formatted according to PhET conventions? See phet-idea-code-style.xml for IntelliJ IDEA code style.

Documentation

[x] Are documentation conventions followed, as described in the “Coding Style Guidelines” section of the PhET Development Overview?
[x] Does model.md adequately describe the model, in terms appropriate for teachers?
[x] Does implementation-notes.md adequately describe the implementation, with an overview that will be useful to future maintainers?
[x] Does the sim build without errors?
[x] Are sim-specific query parameters (if any) identified and documented in one .js file? The .js file should be named QueryParameters, for example ArithmeticQueryParameters for the aritmetic repository.

Common Errors

[x] Is Math.round used where dot.Util.roundSymmetric should be used? Math.round does not treat positive and negative numbers symmetrically, see https://github.com/phetsims/dot/issues/35#issuecomment-113587879
[x] Is toFixed used where dot.Util.toFixed or dot.Util.toFixedNumber should be used? JavaScript's toFixed is notoriously buggy, behavior differs depending on browser, because the spec doesn't specify whether to round or floor.
[x] User interface components with enabled:false should also have pickable:false
[x] Are random numbers using DOT/Random or seedable sources?

Organization, Readability, Maintainability

[x] Does the organization and structure of the code make sense? Do the model and view contain types that you would expect (or guess!) by looking at the sim? Do the names of things correspond to the names that you see in the user interface?
[x] Are appropriate design patterns used?
[x] Is inheritance used where appropriate? Does the type hierarchy make sense?
[x] Is there any unnecessary coupling? (e.g., by passing large objects to constructors, or exposing unnecessary properties/functions)
[x] Is there too much unnecessary decoupling? (e.g. by passing all of the properties of an object independently instead of passing the object itself)?
[x] Are the source files reasonable in size? Scrutinize large files with too many responsibilities - can responsibilities be broken into smaller delegates?
[x] Are any significant chunks of code duplicated? This will be checked manually as well as with https://github.com/danielstjules/jsinspect
[x] Is there anything that should be generalized and migrated to common code?
[ ] Are there any TODO or FIXME comments in the code? They should be addressed or promoted to GitHub issues.
[ ] Does each new common code user interface component that was developed for this sim call Tandem.validateOptions immediately after the options are extended in the constructor? See https://github.com/phetsims/phet-io/issues/77

Performance, Usability

[ ] Does the sim perform as desired across the range of supported platforms? (eg, not too slow on slow platforms, not too fast on fast platforms)
[x] If the sim uses WebGL, does it have a fallback? Does the fallback perform reasonably well? (run with query parameter 'webgl=false')
[ ] Are UI components sufficiently responsive? (especially continuous UI components, such as sliders)
[x] Are pointer areas optimized, especially for touch? (run with query parameter 'showPointerAreas')
[x] Do pointer areas overlap? (run with query parameter 'showPointerAreas')
[x] Is the timestep dt capped appropriately? Try switching applications or browser tabs, then switch back. Did the model take one big/long/awkward step forward? If so, dt may need to be capped. Example from faradays-law.FaradaysLawModel:

// Cap large dt values, which can occur when the tab containing 
// the sim had been hidden and then re-shown
dt = Math.min( 0.1, dt );

Memory Leaks

[ ] Does a heap comparison using Chrome Developer Tools indicate a memory leak? (Describing this process is beyond the scope of this document.)
[x] For each common-code component (sun, scenery-phet, vegas, …) that opaquely registers observers or listeners, is there a call to that component’s dispose function, or documentation about why dispose is unnecessary?
- [x] AXON: Property.link is accompanied by Property.unlink.
- [x] AXON: PropertySet.link is accompanied by PropertySet.unlink.
- [x] AXON: Creation of DerivedProperty is accompanied by dispose.
- [x] AXON: Creation of Multilink is accompanied by dispose.
- [x] AXON: Events.on is accompanied by Events.off.
- [x] AXON: Emitter.addListener is accompanied by Emitter.removeListener.
- [x] SCENERY: Node.addEventListener is accompanied by Node.removeEventListener
- [x] SCENERY: Node.on is accompanied by Node.off
- [x] TANDEM: tandem.addInstance is accompanied by tandem.removeInstance.
Are there leaks due to registering observers or listeners? These guidelines should be followed, or documentation added about why following them is not necessary:
[x] Do all types that require a dispose function have one?

phetsims / plinko-probability

Internal check list in preparation of code review #22

PhET code-review checklist