Cross-origin web pages cannot normally communicate, but <script> requests can pull executable JavaScript around same-origin limits. JSONP uses this loophole to load dynamic data from other origins.

better_errors adds enhanced development error pages with a live REPL, and /__better_errors lets you inspect exceptions from AJAX requests.

Build a RESTful API for ActiveRecord models with very little code. Traim emits a Rack application that can run standalone or inside Rails, but the 1:1 resource model can become limiting.

Rails data can be passed to Unpoly compilers through data-* for simple strings and up-data for objects, arrays, and nested values.

return 444 makes nginx close a connection without sending a response, useful for rejecting specific routes or simulating dropped requests behind a reverse proxy.

Local commits missing from a remote or upstream branch are easy to identify with git cherry -v, which lists the commits not shared by both branches.

Rails 7.1 changes production logging to standard out, which can break file-based logs in opscomplete setups unless the previous logger configuration is restored.

MIME type checks can live in a CarrierWave uploader instead of every mounted model, keeping file-type validation centralized and raising CarrierWave::IntegrityError for bad uploads.

Pending AJAX requests can die when a Capybara test ends or switches scenarios, causing flaky JavaScript specs. Waiting for the page to load helps avoid the failure.

ActiveStorage disk-service requests can clutter development logs with redundant route, record-load, and URL-generation messages. Selective silencing keeps Rails output readable.

pjax loads HTML into the current page without a full reload, preserving permalinks, page titles, and back-button behavior with graceful fallback.

SPF records can be hard to validate, especially when syntax errors or DNS lookup limits break mail delivery. Online checkers help test coverage and new policies before deployment.

Date.today and Date.tomorrow can return the same day when Rails has no configured time zone, causing date handling to drift between UTC and local time.

Running Rails in one file is useful for quick experiments, debugging bugs, or embedding an app in tests, but version and dependency drift can cause surprises.

Rails 4.1 development can ignore newly added I18n YAML files because Spring caches the load path; restarting Spring makes new translations appear.

VCR records real HTTP interactions and replays them from YAML, making network-dependent tests run offline without manual stubs.

Run several MySQL releases side by side in one Linux account for testing or Rails development, using isolated sandboxes on separate ports.

Count and sort request frequencies by client IP in access logs with a short awk pipeline for quick traffic checks and abuse spotting.

Single-threaded Puma in development avoids overlapping requests and noisy console output when debugging. Setting -t 0:1 makes other requests wait.

Chrome can reject locally generated self-signed certificates and hide HTTPS even when they work. Importing the certificate or launching with --ignore-certificate-errors allows testing.