Categories

Categories allow developers to add methods to an existing class without modifying its original file. Borrowed from Objective-C and Smalltalk traditions, categories are used throughout STRVCT to separate concerns—keeping core class files focused on essential logic while adding specialized behaviors in dedicated extension files.

A category is a class that extends the target class but executes .initThisCategory() instead of .initThisClass(). The framework copies the category's prototype and static methods onto the target class's prototype rather than creating a new class entry in the registry.

// SvJsonGroup_patches.js — adds JSON Patch methods to SvJsonGroup
(class SvJsonGroup_patches extends SvJsonGroup {

    applyJsonPatches (patches) {
        // Implementation
    }

    applyPatch (operation) {
        // Single patch operation
    }

}.initThisCategory());

Executing .initThisCategory() instructs the class registration system to merge all prototype and static methods into the parent class (SvJsonGroup). No new class entry is created in the global class registry.

• File & Class Naming: Category files and classes use an underscore to separate the target base class name from the category purpose: SvJsonGroup_patches.js, Array_promises.js, Promise_ideal.js.
• Import Dependency Order: The base class must be listed before its category files in _imports.json:

[
    "SvJsonGroup.js",
    "SvJsonGroup_patches.js",
    "SvJsonGroup_clientState.js"
]

Categories are used heavily during boot to extend native JavaScript objects without polluting the global scope with global functions:

// Promise_ideal.js — adds clone(), status tracking, and timeouts
(class Promise_ideal extends Promise {
    static clone () { /* ... */ }
    callResolveFunc (...args) { /* ... */ }
    isPending () { /* ... */ }
}.initThisCategory());

// Array_promises.js — adds async iteration methods
(class Array_promises extends Array {
    async promiseSerialForEach (aBlock) { /* ... */ }
    async promiseParallelMap (aBlock) { /* ... */ }
}.initThisCategory());

1. No New Slots: Categories can only add methods—they cannot add new slots via initPrototypeSlots(), as prototype slots must be defined during initial class registration.
2. instanceof Compatibility: instanceof checks are completely unaffected. An instance of SvJsonGroup answers true for instanceof SvJsonGroup and does not add a prototype link layer.
3. Full this Access: Category methods execute with full access to this and all slots and methods of the base class.

• Protocols: Interface declaration and conformance checking.
• Style Guide: Coding standards and class patterns.