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Best Practices

A guide for programming well.


  • These are not to be blindly followed; strive to understand these and ask when in doubt.
  • Don't duplicate the functionality of a built-in library.
  • Don't swallow exceptions or "fail silently."
  • Don't write code that guesses at future functionality.
  • Exceptions should be exceptional.
  • Keep the code simple.

Object-Oriented Design

  • Avoid global variables.
  • Avoid long parameter lists.
  • Limit dependencies of an object (entities an object depends on).
  • Limit an object's dependents (entities that depend on an object).
  • Prefer composition over inheritance.
  • Prefer small methods. Between one and five lines is best.
  • Prefer small classes with a single, well-defined responsibility. When a class exceeds 100 lines, it may be doing too many things.
  • Tell, don't ask.


  • Avoid optional parameters. Does the method do too much?
  • Avoid monkey-patching.
  • Generate necessary Bundler binstubs for the project, such as rake and rspec, and add them to version control.
  • Prefer classes to modules when designing functionality that is shared by multiple models.
  • Prefer private when indicating scope. Use protected only with comparison methods like def ==(other), def <(other), and def >(other).

Ruby Gems

  • Declare dependencies in the <PROJECT_NAME>.gemspec file.
  • Reference the gemspec in the Gemfile.
  • Use Appraisal to test the gem against multiple versions of gem dependencies (such as Rails in a Rails engine).
  • Use Bundler to manage the gem's dependencies.
  • Use continuous integration (CI) to show build status within the code review process and to test against multiple Ruby versions.


  • Add foreign key constraints in migrations.
  • Avoid bypassing validations with methods like save(validate: false), update_attribute, and toggle.
  • Avoid instantiating more than one object in controllers.
  • Avoid naming methods after database columns in the same class.
  • Don't change a migration after it has been merged into master if the desired change can be solved with another migration.
  • Don't reference a model class directly from a view.
  • Don't return false from ActiveModel callbacks, but instead raise an exception.
  • Don't use instance variables in partials. Pass local variables to partials from view templates.
  • Don't use SQL or SQL fragments (where('inviter_id IS NOT NULL')) outside of models.
  • Generate necessary Spring binstubs for the project, such as rake and rspec, and add them to version control.
  • If there are default values, set them in migrations.
  • Keep db/schema.rb or db/development_structure.sql under version control.
  • Use only one instance variable in each view.
  • Use SQL, not ActiveRecord models, in migrations.
  • Use the .ruby-version file convention to specify the Ruby version and patch level for a project.
  • Use _url suffixes for named routes in mailer views and redirects. Use _path suffixes for named routes everywhere else.
  • Validate the associated belongs_to object (user), not the database column (user_id).
  • Use db/seeds.rb for data that is required in all environments.
  • Use dev:prime rake task for development environment seed data.
  • Prefer cookies.signed over cookies to prevent tampering.
  • Prefer Time.current over Time.now
  • Prefer Date.current over Date.today
  • Prefer Time.zone.parse("2014-07-04 16:05:37") over Time.parse("2014-07-04 16:05:37")
  • Use ENV.fetch for environment variables instead of ENV[]so that unset environment variables are detected on deploy.
  • Use blocks when declaring date and time attributes in FactoryGirl factories.
  • Use touch: true when declaring belongs_to relationships.


  • Avoid any_instance in rspec-mocks and mocha. Prefer dependency injection.
  • Avoid its, specify, and before in RSpec.
  • Avoid let (or let!) in RSpec. Prefer extracting helper methods, but do not re-implement the functionality of let. Example.
  • Avoid using subject explicitly inside of an RSpec it block. Example.
  • Avoid using instance variables in tests.
  • Disable real HTTP requests to external services with WebMock.disable_net_connect!.
  • Don't test private methods.
  • Test background jobs with a Delayed::Job matcher.
  • Use stubs and spies (not mocks) in isolated tests.
  • Use a single level of abstraction within scenarios.
  • Use an it example or test method for each execution path through the method.
  • Use assertions about state for incoming messages.
  • Use stubs and spies to assert you sent outgoing messages.
  • Use a Fake to stub requests to external services.
  • Use integration tests to execute the entire app.
  • Use non-SUT methods in expectations when possible.


  • Specify the Ruby version to be used on the project in the Gemfile.
  • Use a pessimistic version in the Gemfile for gems that follow semantic versioning, such as rspec, factory_girl, and capybara.
  • Use a versionless Gemfile declarations for gems that are safe to update often, such as pg, thin, and debugger.
  • Use an exact version in the Gemfile for fragile gems, such as Rails.

Relational Databases

  • Index foreign keys.
  • Constrain most columns as NOT NULL.
  • In a SQL view, only select columns you need (i.e., avoid SELECT table.*).
  • Use an ORDER BY clause on queries where the results will be displayed to a user, as queries without one may return results in a changing, arbitrary order.


Background Jobs

  • Store IDs, not ActiveRecord objects for cleaner serialization, then re-find the ActiveRecord object in the perform method.


  • Use SendGrid or Amazon SES to deliver email in staging and production environments.
  • Use a tool like ActionMailer Preview to look at each created or updated mailer view before merging. Use MailView gem unless using Rails version 4.1.0 or later.


  • Avoid rendering delays caused by synchronous loading.
  • Use HTTPS instead of HTTP when linking to assets.


  • Use the latest stable JavaScript syntax with a transpiler, such as babel.
  • Include a to_param or href attribute when serializing ActiveRecord models, and use that when constructing URLs client side, rather than the ID.
  • Prefer data-* attributes over id and class attributes when targeting HTML elements. #462
  • Avoid targeting HTML elements using classes intended for styling purposes. #462


  • Use <button> tags over <a> tags for actions.


  • Document the project's CSS architecture (the README, component library or style guide are good places to do this), including things such as:
    • Organization of stylesheet directories and Sass partials
    • Selector naming convention
    • Code linting tools and configuration
    • Browser support
  • Use Sass.
  • Use Autoprefixer to generate vendor prefixes based on the project-specific browser support that is needed.
  • Prefer overflow: auto to overflow: scroll, because scroll will always display scrollbars outside of macOS, even when content fits in the container.


  • When using sass-rails, use the provided asset-helpers (e.g. image-url and font-url), so that Rails' Asset Pipeline will re-write the correct paths to assets.
  • Prefer mixins to @extend.


  • Avoid supporting versions of Internet Explorer before IE11.


  • Setup new projects using Liftoff and follow provided directory structure.
  • Prefer categories on Foundation classes to helper methods.
  • Prefer string constants to literals when providing keys or key paths to methods.


  • Don't parse the output of ls. See here for details and alternatives.
  • Don't use cat to provide a file on stdin to a process that accepts file arguments itself.
  • Don't use echo with options, escapes, or variables (use printf for those cases).
  • Don't use a /bin/sh shebang unless you plan to test and run your script on at least: Actual Sh, Dash in POSIX-compatible mode (as it will be run on Debian), and Bash in POSIX-compatible mode (as it will be run on OSX).
  • Don't use any non-POSIX features when using a /bin/sh shebang.
  • If calling cd, have code to handle a failure to change directories.
  • If calling rm with a variable, ensure the variable is not empty.
  • Prefer "$@" over "$*" unless you know exactly what you're doing.
  • Prefer awk '/re/ { ... }' to grep re | awk '{ ... }'.
  • Prefer find -exec {} + to find -print0 | xargs -0.
  • Prefer for loops over while read loops.
  • Prefer grep -c to grep | wc -l.
  • Prefer mktemp over using $$ to "uniquely" name a temporary file.
  • Prefer sed '/re/!d; s//.../' to grep re | sed 's/re/.../'.
  • Prefer sed 'cmd; cmd' to sed -e 'cmd' -e 'cmd'.
  • Prefer checking exit statuses over output in if statements (if grep -q ...;, not if [ -n "$(grep ...)" ];).
  • Prefer reading environment variables over process output ($TTY not $(tty), $PWD not $(pwd), etc).
  • Use $( ... ), not backticks for capturing command output.
  • Use $(( ... )), not expr for executing arithmetic expressions.
  • Use 1 and 0, not true and false to represent boolean variables.
  • Use find -print0 | xargs -0, not find | xargs.
  • Use quotes around every "$variable" and "$( ... )" expression unless you want them to be word-split and/or interpreted as globs.
  • Use the local keyword with function-scoped variables.
  • Identify common problems with shellcheck.


In addition to Shell best practices,

  • Prefer ${var,,} and ${var^^} over tr for changing case.
  • Prefer ${var//from/to} over sed for simple string replacements.
  • Prefer [[ over test or [.
  • Prefer process substitution over a pipe in while read loops.
  • Use (( or let, not $(( when you don't need the result


  • Avoid partial functions (head, read, etc).
  • Compile code with -Wall -Werror.


  • Avoid macros.


  • Avoid using $ without scoping to this.$ in views and components.
  • Prefer to make model lookup calls in routes instead of controllers (find, findAll, etc.).
  • Prefer adding properties to controllers instead of models.
  • Don't use jQuery outside of views and components.
  • Prefer to use predefined Ember.computed.* functions when possible.
  • Use href="#" for links that have an action.
  • Prefer dependency injection through Ember.inject over initializers, globals on window, or namespaces. (sample)
  • Prefer sub-routes over maintaining state.
  • Prefer explicit setting of boolean properties over toggleProperty.
  • Prefer testing your application with QUnit.


  • Prefer findWithAssert over find when fetching an element you expect to exist


  • Avoid manual dependency annotations. Disable mangling or use a pre-processor for annotations.
  • Prefer factory to service. If you desire a singleton, wrap the singleton class in a factory function and return a new instance of that class from the factory.
  • Prefer the translate directive to the translate filter for performance reasons.
  • Don't use the jQuery or $ global. Access jQuery via angular.element.


  • Review the recommended practices outlined in Heroku's HTTP API Design Guide before designing a new API.
  • Use a fast JSON parser, e.g. oj
  • Write integration tests for your API endpoints. When the primary consumer of the API is a JavaScript client maintained within the same code base as the provider of the API, write feature specs. Otherwise write request specs.