The Glimmer Reactivity System

Table of Contents

1. Tag Composition: The formal composition semantics of Glimmer's tag-based validation system.
2. The Fundamental Laws of Reactivity: A definition of Glimmer's reliable and consistent reactive programming model, and the rules that reactive abstractions must satisfy in order to safely support this model.
3. System Phases: A description of the phases of the Glimmer execution model: action, render, and idle, and how the exeuction model supported batched UI updates while maintaining a coherent data model.
4. Reactive Abstractions: A description of the implementation of a number of reactive abstractions, and how they satisfy the laws of reactivity.
5. Autotracked Rendering: An overview of the details of how rendering and autotracking interplay.

Pseudocode

This directory also contains pseudocode for the foundation of a reactive system that satisfies these requirements, and uses them to demonstrate the implementation of the reactive abstractions.

• tags.ts: A simple implementation of the tag-based validation system, including an interface for a runtime that supports tag consumptions and tracking frames.
• primitives.ts: Implementation of:
  • Snapshot, which captures a value at a specific revision with its tag validator.
  • PrimitiveCell and PrimitiveCache, which implement a primitive root storage and a primitive cached computation, both of which support law-abiding snapshots.
• composition.ts: Implementations of the higher-level reactive constructs described in Reactive Abstractions in terms of the reactive primitives.

[!TIP]

While these are significantly simplified versions of the production primitives that ship with Ember and Glimmer, they serve as clear illustrations of how to implement reactive abstractions that satisfy the reactive laws.