best-practices

Best Practices

A guide for programming well.

General

• 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.

Ruby

• 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.

Rails

• 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.

Testing

• 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.

Bundler

• 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.

Postgres

• Avoid multicolumn indexes. Postgres combines multiple indexes efficiently. Optimize later with a compound index if needed.
• Consider a partial index for queries on booleans.

Background Jobs

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

Email

• 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.

Web

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

JavaScript

• 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

HTML

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

CSS

• 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.

Sass

• 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.

Browsers

• Avoid supporting versions of Internet Explorer before IE11.

Objective-C

• 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.

Shell

• 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.

Bash

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

Haskell

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

Elixir

• Avoid macros.

Ember

• 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.

Testing

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

Angular

• 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.

Ruby JSON APIs

• 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.