- Angular – Pipes
Formatting values in the template without cluttering the class. `DatePipe`, `CurrencyPipe`, `DecimalPipe` and `AsyncPipe`, chaining pipes and passing arguments, writing a custom pipe, and the pure-versus-impure distinction that decides whether your pipe runs once or on every change detection pass.
- Docker – The Build Context and .dockerignore
`docker build .` uploads that entire directory to the builder before it reads a single instruction — which is why a build can sit for a minute doing apparently nothing. What the context is, why `node_modules` and `target/` must never be in it, and the `.dockerignore` files that took one build from 900 MB of context to 2 MB.
- Hasura – Installation and Your First Query
Get an engine running and a real query answered in one sitting. The Docker Compose service that runs Hasura next to Postgres, why the database port inside the compose network is not the one you published, the admin secret and what it grants, and the console. Then the same thing in v3: installing the `ddn` CLI, `ddn supergraph init` and `ddn run docker-start`.
- Spring Boot – Application Events
Publishing an event instead of calling four services. @EventListener, ordering, async listeners, and @TransactionalEventListener — because a listener that fires before the transaction commits will happily email a customer about an order that is about to be rolled back.
- React – Rendering Lists and Keys
Rendering an array with map, and the key prop React nags you about. What a key is actually for, why the array index is a bug waiting for the list to reorder, what to use when the items have no id, and why keys must be unique among siblings but not globally.