ILIKE searches in PostgreSQL can be slow without trigram indexing; a GIN index with pg_trgm can replace sequential scans with bitmap index scans.

Multi-line Rails logs are hard to filter because only the first line gets tagged. Logging each line separately keeps request IDs and timestamps on every line.

Benchmarking Active Record queries needs repeated runs and cache clearing to measure realistic PostgreSQL performance; a Ruby script can report percentile timings.

rails console --sandbox lets you test database changes in a console session and automatically rolls them back on exit, while file and email actions remain permanent.

validates_uniqueness_of can still allow duplicate records under concurrent requests; a unique database constraint prevents the race and turns collisions into ActiveRecord::RecordNotUnique.

Soft-deleted users can stay authenticated in Devise unless account activity checks are tied to the trash state. Customizing active_for_authentication? blocks sign-in and protects password reset flows.

Terser compresses JavaScript aggressively, merging branches, inlining small functions, and folding constants to cut output size further than expected.

PostgreSQL string ordering follows the C library locale rules, so letters are compared before spaces and punctuation, and case is grouped together.

Run only edited or newly added RSpec files in the current branch by diffing against master, which speeds feedback on focused test changes.

Flaky waitFor tests can fail when Jasmine expectations do not throw, preventing retries. throwUnless and throwUnlessAsync turn failed checks into exceptions for reliable waiting.

Random behavior in Jasmine tests makes results unstable unless spyOn controls dependent calls. returnValue, returnValues, and callFake keep shuffles predictable.

Missing secrets can stay unnoticed in some environments and break behavior later. Using ! on Rails.application.credentials and Rails secrets raises immediately when a value is absent.

Project-specific RuboCop rules can flag conventions and stop the pipeline with little code, such as banning TODO and WIP comments in Ruby files.

301 and 308 redirects can be cached by browsers indefinitely without cache control, making later changes impossible unless users clear their cache.

Date.parse guesses date formats and can accept invalid input, producing unexpected dates. Date.strptime validates against an explicit pattern and avoids ambiguous parsing.

Unsafe ActiveRecord query methods can expose applications to SQL injection when raw SQL is built from untrusted input.

Combining unknown CSS selectors safely fails when a selector list appears; :where() and :not() preserve correct matching without breaking lists.

Detecting when a CSS class is added can be done with a MutationObserver, useful for reacting to DOM state changes on selected elements.

Pinch-zoom, the on-screen keyboard, and other overlays can shift the actually visible page area beyond the layout viewport. VisualViewport exposes the visible region for positioning and tracking.

Start Terminator with split panes and predefined commands while keeping shells open after the command exits.

JavaScript value checks are inconsistent across primitives, objects, arrays, null, undefined, and NaN; the right test depends on whether you need type, instance, or property presence.

Rails uses configurable time zones, while Ruby time APIs follow the server zone and can return wrong results. Time.zone keeps date and time handling consistent.

Business-rule tests with multiple variables can explode into 2n permutations. An n+1 pattern keeps coverage manageable while making individual cases easier to follow.