Documentation Style Guide

Hello! Welcome to the guidelines for writing p5.js documentation. This document is a remix of the following resources:

• Ruby on Rails API Documentation Guidlines (CC BY-SA 4.0)
• WordPress documentation guidelines for accessibility and inclusivity (CC0)
• Airbnb JavaScript Style Guide (MIT)

Our community is large and diverse. Many people learn to code using p5.js, and a large subset of those people are students in K–12 classes. After reading this guide, you will know:

• How to write effective, inclusive, and accessible prose for documentation purposes.
• How to write simple code samples for documentation purposes.

Table of Contents

Writing

• documentation.js and JSDoc
• English
• Oxford Comma
• Wording
• Unbiased Documentation
• Accessibility and Disability

Code

• Code Samples
• Comments
• Accessible Canvas Labels
• Whitespace
• Semicolons
• Naming Conventions
• Variables
• Strings
• Boolean Operators
• Conditionals
• Iteration
• Objects
• Arrays
• Functions
• Arrow Functions
• Chaining
• Classes
• Assets

documentation.js and JSDoc

We use documentation.js to generate the p5.js API documentation from JSDoc comments in the p5.js source code.

Refer to the inline documentation guide for more information on how to structure the documentation comments and what tags to use.

It also discusses how to generate and preview the reference documentation to see your changes.

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English

Please use American English (color, center, modularize, etc). See a list of American and British English spelling differences here.

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Oxford Comma

Please use the Oxford comma ("red, white, and blue", instead of "red, white and blue").

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Wording

Write simple, declarative sentences. Brevity is a plus: get to the point.

Write in the present tense: "Returns an object that...", rather than "Returned an object that..." or "Will return an object that...".

Start comments in upper case. Follow regular punctuation rules:

// Draws a fractal from a Julia set.
function drawFractal(c, radius, maxIter) {
  // ...
}

Communicate the current way of doing things, both explicitly and implicitly. Use the idioms recommended in this guide. Reorder sections to emphasize favored approaches if needed. The documentation should be a model for best practices and approachable for beginners.

Documentation has to be brief but comprehensive. Explore and document edge cases. What happens for each combination of arguments? What bugs are most likely to appear in a beginner's code?

Spell names correctly: p5.js, CSS, HTML, JavaScript, WebGL. When in doubt, refer to an authoritative source like their official documentation.

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Unbiased Documentation

Write documentation without bias towards any kind of person. While documenting particularly demanding/sensitive topics, take the time to educate yourself. Ensure that your writing doesn’t hurt or offend someone unintentionally.

While writing unbiased documentation:

• Be inclusive of every gender identity and expression, sexual orientation, race, ethnicity, language, neuro-type, size, disability, class, religion, culture, subculture, political opinion, age, skill level, occupation, and background. Make examples as diverse as our community.
• Avoid politicized content. If political content is necessary, remain neutral.
• Follow accessibility guidelines.
• Avoid content that would insult or cause harm to people.
• Don’t make any generalizations about people, countries, and cultures. That includes positive or neutral generalizations.
• Don’t write prejudiced and discriminatory content against minority communities.
• Avoid terms related to historical events.

Prefer wordings that avoid "you"s and "your"s. For example, instead of:

If you need to declare a variable, it is recommended that you use `let`.

use this style:

Always use `let` to declare variables.

Pronouns

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Accessibility and Disability

• Emphasize the reader rather than underlining their inconveniences.
• Don’t refer to a person with a disability as a disabled person. Use approved terminology for people with specific disabilities.
• Maintain a uniform structure throughout the p5.js documentation. Emphasize important points both stylistically and visually.
• Use a screen reader to test documentation. To test a screen reader, see List of screen readers.
• Consider multi-platform accessibility for all types of devices and operating systems.
• Create examples with all types of input devices such as voice and gesture based devices, controllers, mice, and keyboards.
• Don’t use ableist language. Be inclusive and unbiased while writing about accessibility and disability.
• Take a pragmatic approach to HTML semantics. Don’t add semantics purely for the sake of semantics. If there is an HTML structure that clearly matches the content, use that element. For example, a group of links should most likely use a list element.
• Use simple tables and tabular formats. Avoid span tags (such as rowspan and colspan). Tables prove to be difficult for screen readers.

Accessibility terminology

The following terminology is adapted from the WordPress documentation guidelines for Writing inclusive documentation. For more background on people-first language, see the CDC's guide on Communicating With and About People with Disabilities.

Code Samples

Choose meaningful code samples that cover the basics as well as gotchas. Only use advanced syntax if it is necessary to explain how a feature works. Don't draw five circles to explain something when one circle will convey the idea. The code samples themselves should follow the guidelines below.

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Comments

• Use // for single line comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment unless it’s on the first line of a block.

// Bad.
let magicWord = 'Please';  // Remember this.

// Good.
// Remember this.
let magicWord = 'Please';

// Bad.
if (keyIsPressed === true) {
  thing1();
  // This is an important note.
  thing2();
}

// Good.
if (keyIsPressed === true) {
  thing1();

  // This is an important note.
  thing2();
}

• Start all comments with a space to make it easier to read.

// Bad.
//Remember this.
let magicWord = 'Please';

// Good.
// Remember this.
let magicWord = 'Please';

• Use // for multiline comments.

// Bad.
/**
 * I will use // for multiline comments.
 * I will use // for multiline comments.
 * I will use // for multiline comments.
 * I will use // for multiline comments.
 * I will use // for multiline comments.
 */

//Bad.
/*
 I will use // for multiline comments.
 I will use // for multiline comments.
 I will use // for multiline comments.
 I will use // for multiline comments.
 I will use // for multiline comments.
 */

// Good.
// I will use // for multiline comments.
// I will use // for multiline comments.
// I will use // for multiline comments.
// I will use // for multiline comments.
// I will use // for multiline comments.

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Accessible Canvas Labels

• Use describe() to in p5.js example code, to add labels to your canvas so that it’s readable for screen readers.

Why? It makes examples accessible to screen readers, and models how to write good canvas labels.

// Good.
function setup() {
  createCanvas(100, 100);
  describe('A red heart in the bottom right corner of a pink background.');
}

// Bad.
function setup() {
  createCanvas(100, 100);
  describe('heart shape');
}

// Good.
function draw() {
  background(220);
  fill(0, 255, 0);
  ellipse(mouseX, 50, 40, 40);
  // Label updates with shape's translation.
  describe(`A green circle at x pos ${round(mouseX)} moving with the mouse pointer.`, LABEL);
}

• Don’t use screen reader labels as a way of commenting your code. Labels should only summarize the resulting visual elements within a canvas.

• Don’t overuse screen reader labels, as you may end up complicating the screen reader’s interpretation of the canvas rather than helping it.

• Do make your label descriptions short and accurate. The recommended length for label descriptions is one to two sentences. Use full sentences for your labels, and write in the present tense when describing elements.

The above examples and suggestions are based on the Writing Accessible Canvas Descriptions tutorial. This tutorial gives more detailed guidance, and includes other ways to label your canvas, in addition to describe(): describeElement(), textOutput(), and gridOutput().

To understand the structure of p5.js’ web accessibility features for contributors, see the Web Accessibility Contributor Doc.

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Whitespace

• Indent blocks 2 spaces.

// Bad.
function setup() {
∙∙∙∙createCanvas(400, 400);
}

// Bad.
function setup() {
∙createCanvas(400, 400);
}

// Good.
function setup() {
∙∙createCanvas(400, 400);
}

• Place 1 space before the leading brace.

// Bad.
function setup(){
  createCanvas(400, 400);
}

// Good.
function setup() {
  createCanvas(400, 400);
}

• Place 1 space before the opening parenthesis in control statements such as if and for. Place no space between the argument list and the function name.

// Bad.
if(keyIsPressed === true) {
  doStuff ();
}

// Good.
if (keyIsPressed === true) {
  doStuff();
}

// Bad.
function setup () {
  createCanvas (400, 400);
}

// Good.
function setup() {
  createCanvas(400, 400);
}

• Place spaces between operators.

// Bad.
let y=x+5;

// Good.
let y = x + 5;

Semicolons

• Yep.

Why? JavaScript's automatic semicolon insertion can lead to subtle bugs.

// Bad.
let x = 0

// Good.
let x = 0;

Naming Conventions

• Avoid single letter names. Be descriptive.

// Bad.
function f(x, y) {
  // ...
}

// Good.
function vectorField(x, y) {
  // ...
}

• Name objects, functions, and instances using camelCase.

// Bad.
let OBJEcttsssss = {};

// Bad.
let this_is_my_object = {};

// Good.
let thisIsMyObject = {};

• Name classes using PascalCase.

// Bad.
class player {
  constructor(name) {
    this.name = name;
  }
}

// Good.
class Player {
  constructor(name) {
    this.name = name;
  }
}

• Don't use trailing or leading underscores.

Why? JavaScript doesn't have private properties or methods.

// Bad.
class Spy {
  constructor(secret) {
    this._secret = secret;
  }
}

// Good.
class Spy {
  constructor(secret) {
    this.secret = secret;
  }
}

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Variables

• Avoid using var to declare variables.

Why? Variables declared with var have confusing scoping rules. These lead to subtle bugs.

// Bad, because it looks reasonable.
circle(x, y, 50);
var x = 200;
var y = 200;

// Good, because it throws a ReferenceError.
circle(x, y, 50);
let x = 200;
let y = 200;

• Always use let to declare variables. Avoid using const.

Why? Variables declared with let are easier to reason about than those declared with var. Variables are often reassigned in sketches, so it's helpful to default to let.

// Bad.
flower = '🌸';
var flower = '🌸';
const flower = '🌸';

// Good.
let flower = '🌸';

• Use one let declaration per variable or assignment.

Why? It’s easier to read and to add new variable declarations.

// Bad.
let positions = getPositions(),
  startSearch = true,
  dragonball = 'z';

// Good.
let positions = getPositions();
let startSearch = true;
let dragonball = 'z';

• Assign variables where needed and place them in a reasonable place.

Why? let is block scoped and not function scoped.

// Bad - unnecessary search.
function getCharacter(name = 'default') {
  let character = characters.find((c) => c.name === name);

  if (name === 'default') {
    return false;
  }

  if (character) {
    return character;
  }
  
  return false;
}

// Good.
function getCharacter(name = 'default') {
  if (name === 'default') {
    return false;
  }

  let character = characters.find((c) => c.name === name);

  if (character) {
    return character;
  }
  
  return false;
}

• Avoid using unary increments and decrements (++, --).

Why? Unary increment and decrement statements are subject to automatic semicolon insertion. This can cause silent errors with incrementing or decrementing values. It's also more expressive to update variables with statements like num += 1 instead of num++.

// Bad.
let num = 1;
num++;
--num;

// Good.
let num = 1;
num += 1;
num -= 1;

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Strings

• Use single quotes '' for strings.

// Bad.
let name = "Hilma af Klint";

// Bad - template literals should contain interpolation or newlines.
let name = `Hilma af Klint`;

// Good.
let name = 'Hilma af Klint';

• Don't concatenate strings that cause the line to go over 80 characters.

Why? Broken strings are hard to read and make code less searchable.

// Bad.
let essay = 'You see us as you want to see us: \
in the simplest terms, in the most convenient definitions.';

// Bad.
let essay = 'You see us as you want to see us: ' +
  'in the simplest terms, in the most convenient definitions.';

// Good.
let essay = 'You see us as you want to see us: in the simplest terms, in the most convenient definitions.';

• Use template strings instead of concatenation when needed.

Why? Template strings have a concise syntax. They also provide proper newlines and string interpolation features.

let name = 'Dave';

// Bad.
text(name + ', this conversation can serve no purpose anymore. Goodbye.' + name, 0, 0);

// Good.
text(`${name}, this conversation can serve no purpose anymore. Goodbye.`, 0, 0);

• Do not unnecessarily escape characters in strings.

Why? Backslashes harm readability.

// Bad.
let bad = '\'this\' \i\s \"quoted\"';

// Good.
let good = 'Air quotes make you look "cool".';

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Boolean Operators

• Use === and !== over == and !=.

• Don't use shortcuts for booleans.

Why? It's easier to understand for beginners.

// Bad.
if (mouseIsPressed) {
  // ...
}

// Good.
if (mouseIsPressed === true) {
  // ...
}

// Bad.
if (name) {
  // ...
}

// Good.
if (name !== '') {
  // ...
}

// Bad.
if (collection.length) {
  // ...
}

// Good.
if (collection.length > 0) {
  // ...
}

• Don't use switch statements unless it's necessary.

• Use parentheses when mixing operators. The only exceptions are the arithmetic operators +, -, and **.

Why? It's easier to read and avoids subtle bugs.

// Bad.
let huh = a && b < 0 || c > 0 || d + 1 === 0;

// Good.
let huh = (a && b < 0) || c > 0 || (d + 1 === 0);

// Bad.
if (a || b && c) {
  return d;
}

// Good.
if (a || (b && c)) {
  return d;
}

// Bad.
let what = a + b / c * d;

// Good.
let what = a + (b / c) * d;

Conditionals

• Use braces with all multiline blocks.

// Bad.
if (mouseIsPressed === true)
  circle(mouseX, mouseY, 50);

// Better.
if (mouseIsPressed === true) circle(mouseX, mouseY, 50);

// Best.
if (mouseIsPressed === true) {
  circle(mouseX, mouseY, 50);
}

• Put else on the same line as the preceding if block’s closing brace.

// Bad.
if (mouseIsPressed === true) {
  thing1();
  thing2();
}
else {
  thing3();
}

// Good.
if (mouseIsPressed === true) {
  thing1();
  thing2();
} else {
  thing3();
}

• Don't use an else block after an if block that always executes a return statement.

// Bad.
function mouseIsOnLeft() {
  if (mouseX < width * 0.5) {
    return true;
  } else {
    return false;
  }
}

// Good.
function mouseIsOnLeft() {
  if (mouseX < width * 0.5) {
    return true;
  }

  return false;
}

• If a condition gets too long, place each (grouped) condition on a new line. The logical operator should begin the line.

Why? It's easier to read.

// Bad.
if ((number === 123 || letters === 'abc') && mouseIsPressed === true && keyIsPressed === true) {
  doStuff();
}

// Good.
if (
  (number === 123 || letters === 'abc')
  && mouseIsPressed === true
  && keyIsPressed === true
) {
  doStuff();
}

• Don't use selection operators in place of conditionals.

  javascriptCopy

  // Bad.
  refrigeratorIsRunning && goCatchIt();
  
  // Good.
  if (refrigeratorIsRunning === true) {
    goCatchIt();
  }
  

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Iteration

• Don’t use while or do-while loops unless it's necessary. Use for loops to iterate a fixed number of times.

let numPetals = 7;

// Bad.
let i = 0;
while (i < numPetals) {
  ellipse(0, 0, 20, 80);
  rotate(PI / numPetals);
  i += 1;
}

// Good.
for (let i = 0; i < numPetals; i += 1) {
  ellipse(0, 0, 20, 80);
  rotate(PI / numPetals);
}

• Don’t use for loops to iterate over arrays.

Why? Pure functions are easier to reason about than side effects.

Use forEach() / map() / every() / filter() / find() / findIndex() / reduce() / some() / ... to iterate over arrays. Use Object.keys() / Object.values() / Object.entries() to produce arrays for iterating over objects.

let diameters = [50, 40, 30, 20, 10];

// Bad.
for (let i = 0; i < diameters.length; i += 1) {
  circle(0, 0, diameters[i]);
}

// Bad.
for (let d of diameters) {
  circle(0, 0, d);
}

// Good.
diameters.forEach((d) => circle(0, 0, d));

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Objects

• Use the literal syntax for object creation.

// Bad.
let ball = new Object();

// Good.
let ball = {};

• Only quote properties that are invalid identifiers.

Why? It's easier to read and improves syntax highlighting. JavaScript engines also have an easier time optimizing for performance.

// Bad.
let secretObject = {
  'x': 100,
  'y': 200,
  'top-secret': 'classified',
};

// Good.
let secretObject = {
  x: 3,
  y: 4,
  'top-secret': 'classified',
};

• Use dot notation to access properties.

let turtle = {
  name: 'Leonardo',
  color: 'dodgerblue',
  weapon: '🗡️',
  food: '🍕',
};

// Bad.
let turtleName = turtle['name'];

// Good.
let turtleName = turtle.name;

• Use bracket notation [] to access properties with a variable.

let turtle = {
  name: 'Leonardo',
  color: 'dodgerblue',
  weapon: '🗡️',
  food: '🍕',
};

function getProp(prop) {
  return turtle[prop];
}

let turtleName = getProp('name');

• Don't use leading commas.

// Bad.
let mathematician = {
    firstName: 'Ada'
  , lastName: 'Lovelace'
};

// Good.
let mathematician = {
  firstName: 'Ada',
  lastName: 'Lovelace',
};

• Add a trailing comma.

// Bad.
let artist = {
  firstName: 'Lauren',
  lastName: 'McCarthy'
};

// Good.
let artist = {
  firstName: 'Lauren',
  lastName: 'McCarthy',
};

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Arrays

• Use the literal syntax for array creation.

// Bad.
let images = new Array();

// Good.
let images = [];

• Use Array#push instead of direct assignment to add items to an array.

let lyrics = [];

// Bad.
lyrics[lyrics.length] = 'Little rough around the edges, but I keep it smooth';

// Good.
lyrics.push('Little rough around the edges, but I keep it smooth');

• Use the slice() method to copy arrays.

// Bad.
let numbersCopy = [];

for (let i = 0; i < numbers.length; i += 1) {
  numbersCopy[i] = numbers[i];
}

// Good.
let numbersCopy = numbers.slice();

• Write arrays on multiple lines when it improves readability. Use line breaks after the opening bracket and before the closing bracket. Add a trailing comma.

// Bad.
let matrix = [[1, 0, 0],
                [0, 1, 0],
                [0, 0, 1]];

// Good.
let matrix = [
  [1, 0, 0],
  [0, 1, 0],
  [0, 0, 1],
];

// Also good.
let matrix = [[1, 0, 0], [0, 1, 0], [0, 0, 1]];

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Functions

• Use function declarations instead of named function expressions.

Why? Function declarations have some gotchas, but they are easier to understand for beginners.

// Bad.
let foo = function () {
  // ...
};

// Bad.
let foo = () => {
  // ...
};

// Good.
function foo() {
  // ...
}

• Use default parameter syntax. Don't mutate function arguments.

// Bad.
function createBall(diameter) {
  diameter = diameter || 50;
  // ...
}

// Good.
function createBall(diameter = 50) {
  // ...
}

• Always put default parameters last.

// Bad.
function drawSpiral(angle = 90, length) {
  // ...
}

// Good.
function drawSpiral(length, angle = 90) {
  // ...
}

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Arrow Functions

• Use arrow function notation for anonymous functions. Callbacks are a common case for this syntax.

Why? The syntax is more concise. It also creates a version of the function that executes in the context of this, which is often helpful.

Why not? If the anonymous function is complex, rewrite it as a declared function.

// Bad.
function setup() {
  loadImage('assets/moonwalk.jpg', function (img) {
    image(img, 0, 0);
  });
}


// Good.
function setup() {
  loadImage('assets/moonwalk.jpg', (img) => {
    image(img, 0, 0);
  });
}

// Bad.
function preload() {
  loadImage('assets/moonwalk.jpg', (img) => {
    // Complex preprocessing...
  });
}

// Good.
function preload() {
  loadImage('assets/moonwalk.jpg', processImage);
}

function processImage(img) {
  // Complex preprocessing...
}

• Use the implicit return when possible. Omit braces if the function body returns a single statement without side effects. Otherwise, keep the braces and use a return statement.

Why? It's easier to read.

// Bad.
[1, 2, 3].map((number) => {
  let squared = number ** 2;
  `${number} squared is ${squared}.`;
});

// Bad.
[1, 2, 3].map((number) => {
  let squared = number ** 2;
  return `${number} squared is ${squared}.`;
});

// Good.
[1, 2, 3].map((number) => `${number} squared is ${number ** 2}.`);

• Always include parentheses around arguments.

Why? Doing so reduces bugs when changing parameters.

// Bad.
[1, 2, 3].map(number => number * number);

// Good.
[1, 2, 3].map((number) => number * number);

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Chaining

• Use individual function calls instead of function chaining.

Why? To accommodate users who may not be familiar with the concept of function chaining.

// Bad.
fill(0)
  .strokeWeight(6)
  .textSize(20);

// Bad.
fill(0).strokeWeight(6).textSize(20);

// Good.
fill(0);
strokeWeight(6);
textSize(20);

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Classes

• Always use class. Avoid manipulating prototype directly. The only exception is explaining how to create libraries.

Why? class syntax is more concise and easier to reason about.

// Bad.
function Mover(x, y, radius) {
  this.x = x;
  this.y = y;
  this.radius = radius;
}

Mover.prototype.update = function () {
  this.x += 1;
  this.y += 1;
};

Mover.prototype.render = function () {
  circle(this.x, this.y, 2 * this.radius);
};

// Good.
class Mover {
  constructor(x, y, radius) {
    this.x = x;
    this.y = y;
    this.radius = radius;
  }

  update() {
    this.x += 1;
    this.y += 1;
  }

  render() {
    circle(this.x, this.y, 2 * this.radius);
  }
}

• Use extends for inheritance.

class RandomMover extends Mover {
  update() {
    this.x += random(-1, 1);
    this.y += random(-1, 1);
  }
}

• Make sure that custom toString() methods don't cause side effects.

// Bad.
class Mover {
  // ...

  toString() {
    this.x += 1;
    return `Mover at (${this.x}, ${this.y})`;
  }
}

// Good.
class Mover {
  // ...

  toString() {
    return `Mover at (${this.x}, ${this.y})`;
  }
}

• Don't write an empty constructor or one that only delegates to a parent class.

Why? Classes have a default constructor if one isn't specified.

// Bad.
class Dot {
  constructor() {}

  render() {
    circle(mouseX, mouseY, 50);
  }
}

// Good.
class Dot {
  render() {
    circle(mouseX, mouseY, 50);
  }
}

// Bad.
class DragonBall extends Ball {
  constructor(x, y, d) {
    super(x, y, d);
  }
}

// Good.
class DragonBall extends Ball {
  constructor(x, y, d, numStars) {
    super(x, y, d);
    this.numStars = numStars;
  }
}

• Avoid duplicate class members.

Why? Duplicate class member declarations prefer the last one. Having duplicates often means there's a bug.

// Bad.
class Mover {
  // ...

  update() {
    this.x += this.xspeed;
    this.y += this.yspeed;
  }

  update() {
    this.x = 0;
    this.y = 0;
  }
}

// Good.
class Mover {
  // ...
  
  update() {
    this.x += this.xspeed;
    this.y += this.yspeed;
  }

  reset() {
    this.x = 0;
    this.y = 0;
  }
}

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Assets

Whether assets (such as images, fonts, sound files, etc) are being used in the descriptions or code examples of the reference documentation, or in tutorials, the same rules apply:

• Always load assets from a folder called assets.
• Store the assets in the public/assets folder of the p5.js-website repository.

Why? It models good project organization. It's also required for assets to load on the p5.js website.

let img;

// Bad.
async function setup() {
  img = await loadImage('moonwalk.jpg');
  //...
}

// Good.
async function setup() {
  img = await loadImage('assets/moonwalk.jpg');
  //...
}

There is more on working with assets in the guide: Contributing to the p5.js reference.

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