Exemplar Code-Review Checklist (a.k.a "CRC") used by PhET Interactive Simulations¶

The responsible dev is responsible for removing the irrelevant parts
A checked-off item doesn't mean "no problem here", it means "it was reviewed"
Problems can be noted in side issues that reference this issue, or through // REVIEW comments in the code

Specific Instructions¶

Provide specific instructions here. For example: known problems that will fail CRC items, files that can be skipped, code that is not completed, shared or common code that also needs to be reviewed,... If there are no specific instructions, then delete this section.

GitHub Issues¶

The following standard GitHub issues should exist. If these issues are missing, or have not been completed, pause code review until the issues have been created and addressed by the responsible dev.

model.md, see {{GITHUB_ISSUE_LINK}}. Familiarize yourself with the model by reading model.md. Does it adequately describe the model, in terms appropriate for teachers? Has it been reviewed by the sim designer?
implementation-notes.md, see {{GITHUB_ISSUE_LINK}}. Familiarize yourself with the implementation by reading implementation-notes.md. Does it provide an overview that will be useful to future maintainers?
results of memory testing for brands=phet, see {{GITHUB_ISSUE_LINK}}
performance testing and sign-off, see {{GITHUB_ISSUE_LINK}}
review of pointer areas, see {{GITHUB_ISSUE_LINK}}
credits (will not be completed until after RC testing), see {{GITHUB_ISSUE_LINK}}

Build and Run Checks¶

If any of these items fail, pause code review.

Does the sim build without warnings or errors?
Does the html file size seem reasonable, compared to other similar sims?
Does the sim start up? (unbuilt and built versions)
Does the sim experience any assertion failures? (run with query parameter ea)
Does the sim pass a scenery fuzz test? (run with query parameters fuzz&ea)
Does the sim behave correctly when listener order is shuffled? (run with query parameters ea&listenerOrder=random and ea&listenerOrder=random&fuzz)
Does the sim output any deprecation warnings? Run with ?deprecationWarnings. Do not use deprecated methods in new code.

Memory Leaks¶

Does a heap comparison using Chrome Developer Tools indicate a memory leak? (This process is described here.) Test on a version built using grunt --minify.mangle=false. Compare to testing results done by the responsible developer. Results can be found in {{GITHUB_ISSUE_LINK}}.
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 is it obvious why it isn't necessary, or is there documentation about why dispose isn't called? An example of why no call to dispose is needed is if the component is used in a ScreenView that would never be removed from the scene graph. Note that it's also acceptable (and encouraged!) to describe what needs to be disposed in implementation-notes.md.
Are there leaks due to registering observers or listeners? The following guidelines should be followed unless documentation (in-line or in implementation-notes.md) describes why following them is not necessary.
AXON: Property.link or lazyLink is accompanied by unlink.
AXON: Multilink.multilink is accompanied by unmultilink.
AXON: Creation of Multilink is accompanied by dispose.
AXON: Creation of DerivedProperty is accompanied by dispose.
AXON: Emitter.addListener is accompanied by removeListener.
AXON: ObservableArrayDef.element*Emitter.addListener is accompanied by ObservableArrayDef.element*Emitter.removeListener
SCENERY: Node.addInputListener is accompanied by removeInputListener
TANDEM: Creation of an instrumented PhetioObject is accompanied by dispose.
All classes that require a dispose function should have one. This should expose a public dispose function that calls this.dispose{{CLASS_NAME}}(), where dispose{{CLASS_NAME}} is a private function declared in the constructor. {{CLASS_NAME}} should exactly match the class name.
All classes that do not properly override dispose should either (a) use isDisposable: false, or (b) implement a dispose method that calls Disposable.assertNotDisposable. Use (a) for classes that inherit a dispose method from Disposable. Use (b) for classes that inherit a dispose method from something other than Disposable. The goal here is to prevent clients from calling dispose for something that does not properly clean itself up, creating a memory leak. This is especially important for common code, but is good defensive programming for sim-specific code.

Performance¶

Play with sim, identify any obvious performance issues. Examples: animation that slows down with large numbers of objects; animation that pauses or "hitches" during garbage collection.
If the sim uses WebGL, does it have a fallback? Does the fallback perform reasonably well? (run with query parameter webgl=false)

Usability¶

Are UI components sufficiently responsive? (especially continuous UI components, such as sliders)
Are pointer areas optimized, especially for touch? (run with query parameter showPointerAreas)
Do pointer areas overlap? (run with query parameter showPointerAreas) Overlap may be OK in some cases, depending on the z-ordering (if the front-most object is supposed to occlude pointer areas) and whether objects can be moved.

Internationalization¶

Does the sim behave correctly with dynamic layout, to support dynamic locale? Run with stringTest=dynamic and use the left/right arrow keys.
Are there any strings that are not internationalized, and does the sim layout gracefully handle internationalized strings that are shorter than the English strings? (run with query parameter stringTest=X. You should see nothing but 'X' strings.)
Does the sim layout gracefully handle internationalized strings that are longer than the English strings? (run with query parameters stringTest=double and stringTest=long)
Does the sim stay on the sim page (doesn't redirect to an external page) when running with the query parameter stringTest=xss? This test passes if sim does not redirect, OK if sim crashes or fails to fully start. Only test on one desktop platform.
Avoid using concatenation to create strings that will be visible in the user interface. Use StringUtils.fillIn and a string pattern to ensure that strings are properly localized. This is relevant in cases where order should be translatable.
Use named placeholders (e.g. "{{value}} {{units}}") instead of numbered placeholders (e.g. "{0} {1}").
Inspect ${REPO}-strings_en.json and verify that all string keys conform to string key conventions. String keys are difficult to change after a sim has been published.
If the sim was already released, make sure none of the original string keys have changed. If they have changed, make sure any changes have a good reason and have been discussed with @jbphet (it is likely that an issue like https://github.com/phetsims/gravity-force-lab/issues/166 should be created).

Repository Structure¶

The repository name should correspond to the sim title. For example, if the sim title is "Wave Interference", then the repository name should be "wave-interference".
Are all required files and directories present? For a sim repository named “my-repo”, the general structure should look like this (where assets/, images/, mipmaps/ or sounds/ may be omitted if the sim doesn’t have those types of resource files).

my-repo/
  assets/
  doc/
    images/
      *see annotation
    model.md
    implementation-notes.md
  images/
    license.json
  js/
    (see section below)
  mipmaps/
    license.json
  sound/
    license.json
  dependencies.json
  .gitignore
  my-repo_en.html
  my-repo-strings_en.json
  Gruntfile.js
  LICENSE
  package.json
  README.md

*Any images used in model.md or implementation-notes.md should be added here. Images specific to aiding with documentation do not need their own license.

Verify that the same image file is not present in both images/ and mipmaps/. If you need a mipmap, use it for all occurrences of the image.
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, where the subdirectory matches the repo name). 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 “Lab”, the general directory structure should look like this:

my-repo/
  js/
  common/
    model/
    view/
  introduction/
    model/
    view/
  lab/
    model/
    view/
  my-repo-main.js
  myRepo.js
  myRepoStrings.js

Coding Conventions¶

Are coding conventions outlined in PhET's Coding Conventions document followed and adhered to? This document deals with PhET coding conventions. You do not need to exhaustively check every item in this section, nor do you necessarily need to check these items one at a time. The goal is to determine whether the code generally meets PhET standards.

TypeScript Conventions¶

Are TypeScript conventions outlined in PhET's TypeScript Conventions document followed and adhered to?

Math Libraries¶

DOT/Utils.toFixed or DOT/Utils.toFixedNumber should be used instead of toFixed. JavaScript's toFixed is notoriously buggy. Behavior differs depending on browser, because the spec doesn't specify whether to round or floor.

IE11¶

IE is no longer supported. With that in mind remove IE-specific workarounds
Use string.includes and string.startsWith where possible.

Organization, Readability, and Maintainability¶

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?
Are appropriate design patterns used? See phet-software-design-patterns.md. If new or inappropriate patterns are identified, create an issue.
Is inheritance used where appropriate? Does the type hierarchy make sense?
Is composition favored over inheritance where appropriate? See https://en.wikipedia.org/wiki/Composition_over_inheritance.
Is there any unnecessary coupling? (e.g., by passing large objects to constructors, or exposing unnecessary properties/functions). If you only need a few fields from a large object, pass them in as separate parameters. The threshold for the number of parameters is up to you - use your judgement. Alternatively in TypeScript, you can decouple by narrowing the API using Pick, but this is a bit of a hack. Here's an example:

class MyClass {
  public constructor( tickMarksVisibleProperty: Property<boolean>,
                      model: Pick<IntroModel, 'changeWaterLevel'>, // <-- Note the call site can pass the whole model, but we declare we will only use this part of it
                      waterCup: WaterCup, modelViewTransform: ModelViewTransform2,
                      providedOptions?: WaterCup3DNodeOptions ) {}
}

Is there too much unnecessary decoupling? (e.g. by passing all of the properties of an object independently instead of passing the object itself)?
Are the source files reasonable in size? Scrutinize large files with too many responsibilities - can responsibilities be broken into smaller delegates? To see file sizes for TypeScript sims, run this shell command:

cd {{repo}}/js ; wc -l `find . -name "*.ts" -print` | sort

Are any significant chunks of code duplicated? In addition to manual identification, tools include: WebStorm Code > Analyze Code > Locate Duplicates and https://github.com/danielstjules/jsinspect.
Is there anything that should be generalized and migrated to common code?
Are there any TODO or FIXME or REVIEW comments in the code? They should be addressed or promoted to GitHub issues.
This means that there should be no TODOs pointing to https://github.com/phetsims/tasks/issues/1129
This means that your repo should have the "todo-should-have-repo" lint rule enabled.
Are there any magic numbers that should be factored out as constants and documented?
Are there any constants that are duplicated in multiple files that should be factored out into a {{REPO}}Constants.js file?
Does the implementation rely on any specific constant values that are likely to change in the future? Identify constants that might be changed in the future. (Use your judgement about which constants are likely candidates.) Does changing the values of these constants break the sim? For example, see https://github.com/phetsims/plinko-probability/issues/84.
Is PhetColorScheme used where appropriate? Verify that the sim is not inventing/creating its own colors for things that have been standardized in PhetColorScheme. Identify any colors that might be worth adding to PhetColorScheme.
Are all dependent Properties modeled as DerivedProperty instead of Property?
All dynamics should be called from Sim.step(dt), do not use window.setTimeout or window.setInterval.

Accessibility¶

This section may be omitted if the sim has not been instrumented with accessibility features. Accessibility includes various features, not all are always include. Ignore sections that do not apply.

General¶

Are accessibility features integrated well into the code? They should be added in a maintainable way, even if that requires upfront refactoring.

Alternative Input¶

Does the sim pass an accessibility fuzz test? (run with query parameters fuzzBoard&ea)
Does the sim use ScreenView.pdomPlayAreaNode.pdomOrder and Screenview.pdomControlAreaNode.pdomOrder to control the traversal order and categorize Nodes in the PDOM? See alternative-input-quickstart-guide.md for more information.
Does this sim use specific keyboard shortcuts that overlap with global shortcuts? This includes the use of modifier keys like in https://github.com/phetsims/ratio-and-proportion/issues/287. NOTE: There is currently no list of global shortcuts, and therefore no way to complete this checklist item. See https://github.com/phetsims/phet-info/issues/188.

Interactive Description¶

Run the entire built sim HTML file through an HTML validator, does the HTML pass?
If applicable, are good design patterns used for interactive description, see interactive-description-technical-guide.md
Does resetting the simulation also reset the entire PDOM?
Make sure accessibility strings aren't being adjusted with ascii specific javascript methods like toUpperCase(). Remember that one day these strings will be translatable
Make sure for accessibility strings that all end of sentence periods do not have a leading space before it. Some screen readers will read these as "dot." This can occur often when a clause is conditionally added.