Contribute 🌸 p5.js Friendly Error System (FES)

🌸 p5.js Friendly Error System (FES)

🌸 p5.js Friendly Error System (FES)


The Friendly Error System (FES, 🌸) aims to help new programmers by providing error messages in simple, friendly language. It supplements your browser’s console error messages by adding an alternative description of the error and links to helpful references.

The FES prints messages in the console window, as seen in the p5.js Web Editor and your browser JavaScript console. The single minified file of p5 (p5.min.js) omits the FES.

Lowering the Barriers to Debugging

The design of a tool should match the need of the people who will use it. As a tool that aims to lower the barriers to debugging, the design of FES is no exception.

The best way to evaluate our existing design is to hear directly from people using p5.js. We ran a community survey in 2021 to gather feedback and future wishes for Friendly Errors.

We believe the insights from our community members will be helpful for our contributors. You can see the results through the summary comic or the full report:

Writing Friendly Error Messages

How to contribute to the p5.js library by writing and translating error messages?

The FES is a part of the p5.js’ internationalization effort. We generate all FES messages’ content through i18next-based translator() function. This dynamic error message generation happens for all languages, including English - the default language of the p5.js.

We welcome contributions from all around the world! 🌐

Writing Best Practices

FES message writers should prioritize lowering the barrier of understanding error messages and increasing the accessibility of debugging process.

Friendly Errors i18n Book discusses challenges and best practices for writing friendly error messages within the cross-cultural i18n context. Here are some points from the book:

  • Understand your audience: do not make assumptions about the audience of our error messages. Try to learn who is using our library and how they use it.
  • Keep language inclusive. We strive to make error messages “friendly,” what does it mean for you? Look for possible bias and harm in your language. Adhere to p5.js Code of Conduct.
  • Use simple sentences whenever possible. Consider breaking your sentence into smaller blocks for best utilizing i18next’s interpolation feature.
  • Prioritize cross-cultural communication and provide a great experience across languages. Avoid using figures of speech.
  • Introduce one technical concept or technical term at a time. Keep consistency in technical writing. Try to link one external resource written in a beginner-friendly language with plenty of short, practical examples.

Friendly Errors i18n Book is a public project, and you can contribute to the book through this separate repo.

Location of Translation Files

translator() is based on i18next and imported from src/core/internationalization.js. It generates messages by looking up text data from a JSON translation file:

translations/{{detected locale code, default=en}}/translation.json

Example: If the detected browser locale is Korean (language designator: ko), the translator() will read in translated text blocks from translations/ko/translation.json. Then translator() will assemble the text blocks into the final message.

The language designator can also include regional information, such as es-PE (Spanish from Peru).

Structure of Translation Files

translation.json has a format used by i18next.

The basic format of a translation file’s item has a key and a value (message) in double quotation marks "", closed by the curly brackets {}:

{ "key": "value" }

For example, we have a ASCII logo saved in this format:

"logo": "    _ \n /\\| |/\\ \n \\ ` ' /  \n / , . \\  \n \\/|_|\\/ \n\n"

i18next supports interpolation, which allows us to pass a variable to generate a message dynamically. We use curly brackets twice {{}} to set a placeholder of the variable:

"greeting": "Hello, {{who}}!"

Here, the key is greeting, and the variable name is who.

To dynamically generate this message, we will need to pass a value:

translator('greeting', { who: 'everyone' } );

The result generated by translator will look like this:

Hello, everyone!

Here is an item from fes’s fileLoadError that demonstrates interpolation:

"image": "It looks like there was a problem loading your image. {{suggestion}}"

To dynamically generate the final message, the FES will call translator() with the key and a pre-generated suggestion value.

translator('fes.fileLoadError.image', { suggestion });

How to Add or Modify Translation

The internationalization doc has a step-by-step guide on adding and modifying translation files.

Understanding How FES Works

In this section, we will give an overview of how FES generates and displays messages. For more detailed information on the FES functions, please see our FES Reference + Dev Notes.


p5.js calls the FES from multiple locations for different situations, when:

  • The browser throws an error.
  • The user code calls a function from the p5.js API.
  • Other custom cases where the user would benefit from a help message.

FES Code Location

You can find the core components of the FES inside: src/core/friendly_errors. You can find the translation files used by the translator() inside: translations/.

FES Message Generators

These functions are mainly responsible for catching errors and generating FES messages:

For full reference, please see our Dev Notes.

FES Message Displayer

fes_core.js/_friendlyError() prints generated friendly error messages in the console. For example:

  translator('fes.globalErrors.type.notfunc', translationObj)

This function can be called anywhere in p5.

Turning Off the FES

There may be cases where you want to disable the FES for performance.

p5.disableFriendlyErrors allows you to turn off the FES when set to true.


p5.disableFriendlyErrors = true;

function setup() {
  createCanvas(100, 50);

The single minified file of p5 (i.e., p5.min.js) automatically omits the FES.