Initial Commit Version on 8/1/2024 is a submission for TCO 2024 Challenge 3

Simple Entity-Component-System

Makes up about a third of the desired final product that should potentially be a little game engine, hopefully in particular for 2D tile-based puzzle games.

Neat JavaScript Tricks / About the Code

The code is written with both features and syntactic sugar from ES6+:

1. class syntax, to it's fullest extent (public and private methods and properties, static initializer blocks, inheritance, etc.)

2. Use of well-known symbols [hasInstance and toPrimitive, mostly] to modify the behaviors of classes.

3. Arrow function/lamba function usage

4. Deliberate use of Maps and Sets for performance gains

5. Array and object destructuring

6. Template strings

7. Reflect.construct, an alternative to Function#apply and Function#call

8. JavaScript's built-in module file organization structure — where every file can be its own library! (not really an accurate description)

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Putting that all aside, there are several cool code tricks (gimmicks, to an extent) scattered throughout the code.

Take a look through:

• index.html for type="importmap" scripts, which let you provide handly aliases for your module files not unlike those you might find in any package manager.

• ECS.mjs for the use of the well-known Symbol.hasInstance alongside JS classes to create "pseudo-types", which helps greatly when you want to test or assert a value's "type" in your code. No more lengthy if-statement conditionals!

• ECS.mjs, containing classes that can't be instantiated directly (at least, not without JavaScript trickery and misdirection — the goal is to help ensure a consistent set of guidelines as to how to use the code, while helping to mitigate simple forgetfulness of said guidelines). Also, use of new.target, a "meta-property" according to MDN.

• ECS.mjs for the use of binary BigInts be the data structure behind Signature as a bitfield/bitset/flag array and pseudo-operator overloading (we can repurpose the bitwise and equality operators with their "intended" purpose on BigInts in order to achieve this)

  • Check out SystemManager.entitySignatureChanged for this in practice ;)

• ECS.mjs for having the Signature class also extend Array, making it so that the index dereference operator works alongside the more safe .set and .reset

• And last but not least, ECS.mjs also makes use of the optional chaining operator ?. in order to check whether an object is actually a class object that is the sub-class of another (class B extends A, B?.prototype instanceof A)

• Take a peek at Helper.mjs to see how simply we can implement the method chaining used in assert and integer.

• Helper.mjs also includes use of CSS.supports to help with determining whether a given string is a legal value for canvas fill styles.

• In Types.mjs, there's four primitive pseudo-types integer, char, null, and array for use with expect

• Everywhere assert is used, there's a "mark" with the optional chaining operator that has no effect on the code's behavior but is useful for indicating which instances of assert are utilized me for debugging or for the end user to assist with proper usage. temporary ones will be removed for the user-dev version, and interface ones will be removed for the user-production version

What Next?

• The current status quo of writing code with the ECS module includes a lot of boilerplate registering components and systems and setting signatures. Ideally I'd write a parser for a file format to allow a data driven format where the data, default values, behavior, signatures, and classes can all be defined simply in one place. The boilerplate and code would then be generated.

  • Ideally a priority ordering for the execution of the systems would also be implemented, because they have to happen sequentially one way or another.

• Provide default implementations of commonly used components and systems?

  • Transform, Drawable, RigidBody?

  • Physics? (2D)Renderer?

  • Systems have Component dependencies. Can Systems have System dependencies? (And is that the same thing as just having a priority ordering? Is there any reason to have a dependency that executes AFTERwards?) Can Components have System dependencies?

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TODO:

☑	Find out whether there's anywhere expect can be used, perhaps with assert or if-statements
☐	Write the rest of this README, continuing from Helper.mjs
☑	Comment the code as necessary