Angular Migrations (v18 through v21)

Core Philosophy

Upgrade one major version at a time — skipping versions risks missing migration schematics and accumulating unresolved breaking changes.
Run official schematics before manual fixes — Angular provides automated migrations for most breaking changes; manual work is the last resort.
Signals, standalone, and zoneless are the destination — every migration should move closer to the modern Angular paradigm, not just fix compilation errors.
Test at every step — run ng build, ng test, and e2e after each version bump before proceeding.
Treat migration as architecture, not syntax — version upgrades after v18 are architectural shifts (reactivity model, change detection, module system), not just API renames.

Starting Version	Target	Key Theme	Reference
v18	v19	Standalone default, signals stable	`references/v18-to-v19.md`
v19	v20	Build system change, Karma removed	`references/v19-to-v20.md`
v20	v21	Zoneless default, Vitest, Signal Forms	`references/v20-to-v21.md`
Any	Signals	Decorator→signal function migration	`references/signals-migration.md`
Any	Zoneless	Zone.js removal strategy	`references/zoneless-migration.md`