Fron-tend Guidelines

A one-page document to help your team establish effective frontend guidelines, so that you can write consistent & cohesive code together.

HTML

HTML Principles

What are some general principles your team should follow when writing HTML? (for example, authoring semantic HTML5 markup, accessibility, etc. See these resources for inspiration)

HTML Tools

Sass preprocessor and SCSS syntax for stylesheet files, using .scss extension
What template engine your team should use? (e.g. Nunjucks)
What CI and task runner? (e.g. Gulp to run a helpful tasks such as: compiling your Sass files to CSS, processing assets files (JS, images,icons), optimizing and building files for production and more)
Fractal for components library and style guide

HTML Style

Indent yout code using 2 spaces, not tabs
Use comments carefully defining start and end of a block in a way like:  
What order to follow for classnames?

CSS

Principles

What are some general principles your team should follow when writing CSS? (For example, modularity, avoiding long selector strings, etc. See these resources for inspiration)

Methodology

We adopt BEM methodology.

Are you deviating from the methodology in any way? If so, can you highlight these conventions?

Tools

Is the team using a preprocessor (such as Sass or Less)?
What are the guidelines for using that preprocessor (check out Sass Guidelines for inspiration)?
Are you using a CSS base (such as Normalize or a reset)?
Are you using any CSS postprocessors (such as Prefixfree or Autoprefixer)?
Are you using CSS Custom Properties? If so, explaing the difference with Sass variables
Are there specific CSS techniques you're utilizing (such as critical CSS)?

Common rules

two (2) spaces indents, no tabs;
80-characters wide lines;
one space before the opening brace of declaration blocks for legibility
Place closing braces of declaration blocks on a new line
Include one space after : for each declaration
Each declaration should appear on its own line for more accurate error reporting
End all declarations with ;. The last declaration's is optional, but your code is more error prone without it.
Comma-separated property values should include a space after each comma
Lowercase all hex values, e.g., #fff
Use shorthand hex values where available, e.g., #fff instead of #ffffff.

/* Bad CSS */
.selector, .selector-secondary, .selector[type=text] {
  padding:15px;
  margin:0px 0px 15px;
  background-color:rgba(0, 0, 0, 0.5);
  box-shadow:0px 1px 2px #CCC,inset 0 1px 0 #FFFFFF
}

/* Good CSS */
.selector,
.selector-secondary,
.selector[type="text"] {
  padding: 15px;
  margin-bottom: 15px;
  background-color: rgba(0,0,0,.5);
  box-shadow: 0 1px 2px #ccc, inset 0 1px 0 #fff;
}

Declaration sorting

Related property declarations should be grouped together following the order:

Positioning
Box model
Typographic
Visual
Misc

.declaration-order {
  /* Positioning */
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 100;

  /* Box-model */
  display: block;
  float: right;
  width: 100px;
  height: 100px;

  /* Typography */
  font: normal 13px "Helvetica Neue", sans-serif;
  line-height: 1.5;
  color: #333;
  text-align: center;

  /* Visual */
  background-color: #f5f5f5;
  border: 1px solid #e5e5e5;
  border-radius: 3px;

  /* Misc */
  opacity: 1;
}

Positioning comes first because it can remove an element from the normal flow of the document and override box model related styles. The box model comes next as it dictates a component's dimensions and placement.

Everything else takes place inside the component or without impacting the previous two sections, and thus they come last.

Use PostCSS VSCode Plugin to automatically sorting your code with this configuration. Copy settings in your VSCode settings.json.

Indenting

When indenting in Sass, stick two(2) spaces and leave a blank line before and after the nested ruleset:

foo {
  color: red;

  .bar {
    color: blue;
  }

}

Selector Nesting in Sass

Avoid selector nesting as much as possible. The problme is that it makes code more difficult to read.

Don't nest more than 3 leves deep, following the Inception Rule
Use along with BEM naming convention to generate .block_element

Encoding

To avoid any potential issue with character encoding, it is highly recommended to force UTF-8 encoding in the main stylesheet using the @charset directive. Make sure it is the very first element of the stylesheet and there is no character of any kind before it.

@charset 'utf-8'

Quotes

Wrap Sass strings in single quotes.

// Yep
$direction: 'left';

// Nope
$direction: left;

Strings as CSS values

Specific CSS values (identifiers) such as initial or sans-serif require not to be quoted

// Yep
$font-type: sans-serif;

// Nope
$font-type: 'sans-serif';

Strings containing quotes

If a string contains one or several single quotes, one might consider wrapping the string with double quotes (") instead, in order to avoid escaping characters within the string.

// Yep
@warn "You can't do that.";

URLs

URLs should be quoted as well, for the same reasons as above:

// Yep
.foo {
  background-image: url('/images/kittens.jpg');
}

// Nope
.foo {
  background-image: url(/images/kittens.jpg);
}

Units & Numbers

Numbers shouldn't display leading zeros before a decimal value less than one.
When dealing with lengths, a 0 value should never ever have a unit (e.g., margin: 0; instead of margin: 0px;)
Don't prefix property values or color parameters with a leading zero (e.g., .5 instead of 0.5 and -.5px instead of -0.5px)

// Yep
.foo {
  padding: 2em;
  opacity: .5;
  margin: 0;
}

// Nope
.foo {
  margin: 0em;
  padding: 2.0em;
  opacity: 0.5;
}

Calculations

Top-level numeric calculations should always be wrapped in parentheses.

// Yep
.foo {
  width: (100% / 3);
}

// Nope
.foo {
  width: 100% / 3;
}

Colors

Respect the following order of preference for color formats:

HSL notation;
RGB notation;
HEX notation (lowercase and shortened);

// Yep
.foo {
  color: hsl(0, 100%, 50%);
}

// Also yep
.foo {
  color: rgb(255, 0, 0);
}

// Meh
.foo {
  color: #f00;
}

// Nope
.foo {
  color: #FF0000;
}

// Nope
.foo {
  color: red;
}

When using HSL or RGB notation, always add a single space after a comma (,) and no space between parentheses ((, )) and content.

// Yep
.foo {
  color: rgba(0, 0, 0, 0.1);
  background: hsl(300, 100%, 100%);
}

// Nope
.foo {
  color: rgba(0,0,0,0.1);
  background: hsl( 300, 100%, 100% );
}

Color Variables

Store color variables in another variable with a name explaining how it should be used:

$main-theme-color: $sass-pink;

Maps

Maps should be written as follows:

space after the colon (:);
opening brace (() on the same line as the colon (:);
quoted keys if they are strings (which represents 99% of the cases);
each key/value pair on its own new line;
comma (,) at the end of each key/value;
trailing comma (,) on last item to make it easier to add, remove or reorder items;
closing brace ()) on its own new line;
no space or new line between closing brace ()) and semi-colon (;).

// Yep
$breakpoints: (
  'small': 767px,
  'medium': 992px,
  'large': 1200px,
);

// Nope
$breakpoints: ( small: 767px, medium: 992px, large: 1200px );

JavaScript

JavaScript Principles

What are some general principles your team should follow when writing JavaScript? (See these resources for inspiration)

JavaScript tools

Are you using a JavaScript framework (such as jQuery, Ember, Angular, etc)?
Where is the documentation for those frameworks?
Are you using any polyfills or shims (such as any of these)?
What third-party scripts are dependencies for your project (such as scripts for form validation, graphs, animation, etc)?
Do you test your JavaScript? If so, what tools do you use (such as Jasmine, Karma, Selenium, etc)?

JavaScript Style

(See these resources for inspiration)

Spaces or Tabs?
What does JS commenting look like?
What patterns are you following? (See these resources)

Media

How are you handling icons (such as using SVG, icon fonts, etc)?
How are you handling responsive images (such as using srcset & <picture />)?
Are you using any tools to optimize and serve images?

Fonts

How do you load custom fonts?
Do you use any tools to help implement web fonts (such as Font Squirrel, etc)?
Do you use a service to manage and serve custom fonts (such as Fonts.com, Typekit, etc)?

Performance

Do you use performance budgets? If so, what metrics are you using to determine budgets? Where are you keeping track of performance budgets?
How are you measuring your project's speed (such as Pingdom Speed Test or Google PageSpeed)?
What techniques are you using to decrease file size (such as Gzip, Image Optimization)?
What performance-related tools are you using in your workflow? (such as WebPagetest, BigRig Speedcurve)?

Accessibility

Are you following the accessibility recommendations laid out in this checklist?
What accessibility-related tools are you using in your workflow?

Tooling

Are you using a task runner (such as Grunt or Gulp)?
Are you using a dependency manager (such as Bower or Composer)?
Are you using any scaffolding tools (such as Yeoman)?
Are you using any tools to reinforce frontend style (such as Editor Config or linters)?
Are any other specific pieces of software that are needed to work on this project?

Version control

What version control system are you using for your frontend code (such as Git or Subversion)?
Where is your version-controlled code hosted (such as Github or Bitbucket)?
Do you use a version control workflow (such as gitflow, centralized, feature-branch, etc)?
Who's responsible for managing and governing the version controlled code??
Where are issues tracked?

Support and Optimization

It's important to recognize the difference between "support" and "optimization". You should do your best to support as many environments as possible while simultaneously optimizing for the environments that make the most sense for your business and users.

What browsers are you optimizing for?
What devices are you optimizing for?
Are you using a graded browser support system?
Are there specific components that require more specific grading?

Localization

Is your website served in different languages? If so, what considerations do you need to address when localizing for other languages?

Deployment/Integration

How is your front-end code integrated into a production environment?

Documentation

Are you using a pattern library tool to document your front-end architecture?
Where does your documentation live? What are the links to the documentation?
Who's responsible for maintaining and governing the documentation?
What happens when the guidelines are updated?

Feel free to modify or extend (such as adding specific sections for performance, accessibility, etc) this document for your own organization's needs. For questions, comments, additions, and corrections, please open an issue on Github and/or reach out to @brad_frost on Twitter.

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