Rack::SteadyETag generated stable ETags for responses that only changed in CSRF tokens or CSP nonces. Rails apps should be configured to return identical HTML for the same resource and user.

Rails default ETags often never repeat because rotating CSRF tokens and CSP nonces change response bytes, blocking cache hits and 304 responses.

in and of mean different things in CoffeeScript and JavaScript, making property checks and iteration easy to mix up.

Common Rails nested form pitfalls include missing accepts_nested_attributes_for, wrong form helper scope, and lost parameters that prevent child records from saving.

Dogmatic red-green-refactor TDD can be tedious; a pragmatic mix of integration and unit tests uses scenario titles as a todo list and supports iterative development.

Individual transform properties make CSS transforms easier to read, animate, and maintain, with broad browser support for scale, rotate, and translate.

asdf manages multiple runtime versions through one CLI and supports legacy version files like .nvmrc and .ruby-version for smoother migration from rbenv.

Async rejections can fail Jasmine tests as unhandled promise rejections when the promise is not awaited or returned. jasmine.spyOnGlobalErrorsAsync() lets tests ignore or inspect the global error.

Cron jobs sometimes need to run on exactly one server or on every server; whenever_roles can separate shared tasks from single-host tasks.

Plain text .erb emails preserve indentation and blank lines, so indented template code can insert unwanted spaces or extra newlines. Trim mode and unindented markup prevent formatting bugs.

Limit a test run to one example or group with :focus, fit, fdescribe, or fcontext; unfocused suites fall back to running everything.

CSP nonce-based policies can replace brittle host allowlists, while strict-dynamic lets trusted scripts load additional scripts in modern browsers.

Custom Jasmine matchers add reusable expectations for tests, including tailored pass/fail logic and clearer failure messages.

Processing large record sets can exhaust memory when loading everything at once. find_in_batches and find_each keep memory usage lower for long-running data updates.

calc() enables CSS values to combine percentages and absolute units, such as sizing an element to fit a container with fixed side margins.

irb and rails console can crash unpredictably because of multi-line autocomplete; disabling it may stop the failures.

Sidekiq 7 capsules let queues run with separate concurrency limits, useful for protecting apps or APIs from too many parallel jobs.

Oklch keeps derived colors aligned as a base color changes, preserving contrast more reliably than RGB or HSL for accessible palettes.

Unused and duplicate database indexes can slow writes, waste storage, and complicate maintenance in PostgreSQL; SQL one-liners help identify candidates for cleanup.

Large Sass/SCSS maps become hard to read when they grow, and multiline map syntax is unsupported in .sass. Using .scss avoids parser errors.

RubyMine test navigation depends on marking test folders as Test Sources Root; remapping CTRL + ALT + SHIFT + c can copy repository-relative paths like spec/foo_spec.rb instead of foo_spec.rb.

Browser support in Webpacker depends on both Babel and UglifyJS; mismatched settings can break legacy browsers like IE11 even when JavaScript is transpiled.

Transparent apple-touch-icon images on iOS turn black in Safari, so solid backgrounds prevent ugly home-screen and bookmark icons.

Haml 6 renders most custom attributes verbatim, so falsy values no longer remove them. Boolean attributes keep special handling, and Haml::BOOLEAN_ATTRIBUTES can extend that list.