• Syntax
• HTML doctype
• Language attribute
• Character encoding
• CSS and JavaScript includes
• Practicality over purity
• Boolean attributes
• Reducing markup
• JavaScript generated markup

• CSS syntax
• Declaration order
• Don't use @import
• Media query placement
• Prefixed properties
• Shorthand notation
• Comments
• Class names

• JavaScript style & syntax
• Function Naming
• Function Design
• Widget Structure
• Comments
• Opening example in Codepen

These standards are provided as a guide to contributing to W3C WAI-ARIA APG

They are based on Code Guide by @mdo.

The following priorities have been used to determine these standards:

1. Readability / understandability
2. Familiarity
3. Ease of maintenance
4. Ease of contribution
5. Performance

• Latest version of Google Chrome
• Latest version of Mozilla Firefox

• Use soft tabs with two spaces—they're the only way to guarantee code renders the same in any environment.
• Nested elements should be indented once (two spaces).
• Always use double quotes, never single quotes, on attributes.
• Don't include a trailing slash in self-closing elements—the HTML standard says they're optional.
• Don’t omit optional closing tags (e.g. </li> or </body>).

Enforce standards mode and more consistent rendering in every browser possible with this simple doctype at the beginning of every HTML page.

From the HTML standard:

Authors are encouraged to specify a lang attribute on the root html element, giving the document's language. This aids speech synthesis tools to determine what pronunciations to use, translation tools to determine what rules to use, and so forth.

Read more about the lang attribute in the spec.

Head to Sitepoint for a list of language codes.

Use UTF-8, and use the short form <meta charset="UTF-8"> as the first child in head.

Per the HTML standard, there is no need to specify a type when including CSS and classic JavaScript files as text/css and text/javascript are their respective defaults.

• Using link
• Using style
• Using script

Strive to maintain HTML standards and semantics, but not at the expense of practicality. Use the least amount of markup with the fewest intricacies whenever possible.

A boolean attribute is one that needs no declared value. XHTML required you to declare a value, but HTML has no such requirement.

For further reading, consult the WHATWG section on boolean attributes:

The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If you must include the attribute's value, and you don't need to, follow this WHATWG guideline:

If the attribute is present, its value must either be the empty string or [...] the attribute's canonical name, with no leading or trailing whitespace.

In short, don't add a value.

Whenever possible, avoid superfluous parent elements when writing HTML. Many times this requires iteration and refactoring, but produces less HTML. Take the following example:

Writing markup in a JavaScript file makes the content harder to find, harder to edit, and less performant. Avoid it whenever possible.

• All CSS must be compatible with the latest release of Chrome, Firefox, and Safari.
• Use soft tabs with two spaces—they're the only way to guarantee code renders the same in any environment.
• When grouping selectors, keep individual selectors to a single line.
• Include 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 a semi-colon. 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 (e.g., box-shadow).
• Don't include spaces after commas within rgb(), rgba(), hsl(), hsla(), or rect() values. This helps differentiate multiple color values (comma, no space) from multiple property values (comma with space).
• Do prefix property values or color parameters with a leading zero (e.g., 0.5 instead of .5 and -0.5px instead of -.5px).
• Lowercase all hex values, e.g., #fff. Lowercase letters are much easier to discern when scanning a document as they tend to have more unique shapes.
• Use shorthand hex values where available, e.g., #fff instead of #ffffff.
• Quote attribute values in selectors, e.g., input[type="text"]. They’re only optional in some cases, and it’s a good practice for consistency.
• Avoid specifying units for zero length values, e.g., margin: 0; instead of margin: 0px;. (Note that values that are not lengths still require a unit, e.g. 0deg.)

Questions on the terms used here? See the syntax section of the Cascading Style Sheets article on Wikipedia.

Related property declarations should be grouped together following the order:

1. Positioning
2. Box model
3. Typographic
4. Visual

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.

For a complete list of properties and their order, please see Recess.

Compared to <link>s, @import is slower, adds extra page requests, and can cause other unforeseen problems. Avoid them and instead opt for an alternate approach:

• Use multiple <link> elements
• Compile your CSS with a preprocessor like Sass or Less into a single file
• Concatenate your CSS files with features provided in Rails, Jekyll, and other environments

For more information, read this article by Steve Souders.

Place media queries as close to their relevant rule sets whenever possible. Don't bundle them all in a separate stylesheet or at the end of the document. Doing so only makes it easier for folks to miss them in the future. Here's a typical setup.

When using vendor prefixed properties, indent each property such that the declaration's value lines up vertically for easy multi-line editing.

In Textmate, use Text → Edit Each Line in Selection (⌃⌘A). In Sublime Text 2, use Selection → Add Previous Line (⌃⇧↑) and Selection → Add Next Line (⌃⇧↓).

Strive to limit use of shorthand declarations to instances where you must explicitly set all the available values. Common overused shorthand properties include:

• padding
• margin
• font
• background
• border
• border-radius

Often times we don't need to set all the values a shorthand property represents. For example, HTML headings only set top and bottom margin, so when necessary, only override those two values. Excessive use of shorthand properties often leads to sloppier code with unnecessary overrides and unintended side effects.

The Mozilla Developer Network has a great article on shorthand properties for those unfamiliar with notation and behavior.

Code is written and maintained by people. Ensure your code is descriptive, well commented, and approachable by others. Great code comments convey context or purpose. Do not simply reiterate a component or class name.

Be sure to write in complete sentences for larger comments and succinct phrases for general notes.

• Keep classes lowercase and use dashes (not underscores or camelCase). Dashes serve as natural breaks in related class (e.g., .btn and .btn-danger).
• Avoid excessive and arbitrary shorthand notation. .btn is useful for button, but .s doesn't mean anything.
• Keep classes as short and succinct as possible.
• Use meaningful names; use structural or purposeful names over presentational.
• Prefix classes based on the closest parent or base class.
• Use .js-* classes to denote behavior (as opposed to style), but keep these classes out of your CSS.

It's also useful to apply many of these same rules when creating Sass and Less variable names.

All JavaScript must be compatible with the latest release of Chrome, Firefox, and Safari.

Please refer to the AirBnB Javascript Style Guide for all basic javascript syntax and code style rules.

1. Functions that return booleans should be prefixed with is, has, are or similar keywords distinguish the return value, (e.g: isVisible, areEqual, hasEncryption).

   function isVisible(element) {
     return element.classList.contains('open');
   }
   
   function areEqual(a, b) {
     // function logic
     return a === b;
   }
   
   function hasEncryption() {
     // function logic
     return encryption === true;
   }

2. Functions that return HTML snippets should be prefixed with render, for example:

   function renderButton(label) {
     return `<button type="button">${label}</button>`;
   }

3. Functions that are intended to be event handlers should be prefixed with on, e.g. onKeyDown. If the event handler is specifically for one element within a complex widget, include the element name as well: onButtonClick.

   mainEl.addEventListener('click', onClick);
   buttonEl.addEventListener('click', onButtonClick);
   listboxEl.addEventListener('keydown', onListboxKeyDown);

4. Functions that mutate state should be prefixed with update, or a verb that describes the state change. The full function name should be in the format of "verb + name of state" For example, openListbox or updateFilterString.

   function openListbox() {
     this.listbox.open = true;
   }
   
   function updateFilterString(value) {
     this.filterString = value;
   }
   
   function updateActiveOption(index) {
     this.activeOption = index;
   }

5. Be specific when naming functions so that whenever possible, the function name is descriptive on its own without needing additional comments to clarify. Prefixing function names with verbs is a good practice.

   - function buttonLabel(label) {
   -	...
   - }
   + function applyButtonLabel(label) {
   +	...
   + }

Ideally functions should be single-purpose, short, and avoid side effects. The goal is to write functions that are easy to read, test, and refactor.

1. Pure functions and side effects: whenever possible, computation and logic should be handled in pure functions, or functions that do not depend on or mutate external state. Functions that do modify external state should follow an update* naming convention as described in the "Function Naming" section. For example, combobox logic to filter options as a user types could be split out as follows:

   - function onInput(event) {
   -	  // logic here to get an array of filtered options based on event.target.value and this.options
   -	  const filteredOptions = result;
   -
   -   // logic here to update internal state and the DOM, e.g.:
   -   this.options = filteredOptions;
   -   this.listboxEl.innerHTML = '';
   -   filteredOptions.forEach((option) => {
   -     // etc
   -     this.listboxEl.appendChild(newOptionEl);
   -   });
   - }
   + function onInput(event) {
   +	  const filteredOptions = this.filterOptions(event.target.value, this.options);
   +   this.updateOptions(filteredOptions);
   + }
   +
   + function filterOptions(filterString, optionArray) {
   +	  // logic here to do actual filtering
   +   // this is the "pure" function
   +   return result;
   + }
   +
   + function updateOptions(optionArray) {
   +	  this.options = filteredOptions;
   +   // optionally split this logic into a renderListbox() function
   +   // this makes sense to split out if there are any other actions that would result in updating the listbox HTML without also updating this.options
   +   this.listboxEl.innerHTML = '';
   +   filteredOptions.forEach((option) => {
   +     // etc
   +     this.listboxEl.appendChild(newOptionEl);
   +   });
   + }

2. Single-purpose functions: avoid double-barrelled functions, for example setFocusAndDoStuff(). Calling setFocus() and doStuff() makes the logic for each step easier to read and understand. Ideally this also makes them easier to name and potentially refactor.

   - function onOptionClick(event) {
   -	  this.closeListboxAndUpdateValue(event.target.innerText);
   - }
   -
   - function closeListboxAndUpdateValue(newValue) {
   -	  // logic here to update listbox state
   -   // ...
   -
   -   // logic here to update the listbox value
   -   buttonEl.innerText = newValue;
   - }
   + function onOptionClick(event) {
   +	  this.closeListbox();
   +   this.updateValue(event.target.innerText);
   + }
   +
   + function closeListbox(event) {
   +	  // logic here to update listbox state
   +   // ...
   + }
   +
   + function updateValue(event) {
   +	  // logic here to update the listbox value
   +   buttonEl.innerText = newValue;
   + }

3. Avoid nested conditionals and ternaries

   - function getResult() {
   -   let result;
   -   if (A) {
   -     result = resultA();
   -	  } else {
   -     if (B) {
   -       result = resultB();
   -     } else {
   -       if (C) {
   -         result = resultC();
   -       } else {
   -         result = resultD();
   -       }
   -     }
   -   }
   -   return result;
   - }
   -
   + function getResult() {
   +   if (A) return resultA();
   +   if (B) return resultB();
   +   if (C) return resultC();
   +   return resultD();
   + }

When writing the javascript for a new widget, there are certain guidelines for code organization and structure to maintain consistency with other APG widgets.

1. Widgets should be defined as classes, with one class per widget.

2. Internal variables and functions should be in the following order within the widget class, and sorted alphabetically:

   1. Constructor function
      1. Properties
      2. State variables
   2. All other functions

3. Widgets should not be written to expose any of their internal state variables or functions. Communication should be done through emmitting events and handling property updates.

4. Here is a basic skeleton for creating a new widget class:

   /*
   *   This content is licensed according to the W3C Software License at
   *   https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document
   */
   
   'use strict';
   
   class Cat {
     constructor(el, name) {
       // properties
       this.el = el;
       this.name = name;
   
       // states
       this.isPurring = false;
       this.isSleeping = false;
     }
   
     onPet(event) {
       // etc
     }
   
     renderCat() {
       // create DOM
       // attach event handlers
       // etc.
     }
   
     updatePurring(purring) {
       this.isPurring = true;
     }
   
     // etc.
   }

1. Refer to the AirBnB comment styles for comment formatting.
2. Avoid adding comments that just duplicate information in a function name or variable name.
3. Comments should not explain "what" something is doing, but rather the "why".
4. JSDoc comments are not needed