In-browser editor for p5.js with live reloading, tightening the creative feedback loop.
I was motivated to develop p5-webeditor because I wanted to reduce the friction between having an idea to explore in p5 and being able to see it live. Being able to quickly try a concept without setting up a new project is powerful; so is not needing to refresh the page every few seconds after making short edits. The power of p5 is that it runs in a browser environment, and this project hopes to leverage that into a more fluid experience.
Initially, my two main interface goals were:
- Intelligent reloading
- Reloading the sketch disrupts flow, and should happen as infrequently as possible in order to keep the canvas up to date. In particular, the sketch should never reload on syntactically invalid/unfinished code that a user would not have intended to reload.
- Code persistence
- Ever filled out a form and accidentally pressed the back button and lost everything? The editor should regularly save state and act as a metaphorical sketchbook.
The technical challenges that came up around executing code from user input in the browser raised more interesting opportunities to develop those general goals into informed implementation decisions.
On each text change event, p5-webeditor checks the text deltas to make sure they are not insignificant edits, like whitespace or semicolons. If there are significant edits, a timeout will be set to fire after typing has paused. The timeout runs the code through JSHint, which will run static analysis on the code to check for errors. JSHint is configured to suppress most warnings and only raise for fatal errors like syntax or undefined symbols. It is also configured to understand that the code has p5.prototype's fields in global variable scope.
Once the code passes both the delta and static analysis filters, the code is stored in memory and in localstorage, in order to persist across browser sessions (and survive accidental back button navigation). p5-webeditor will then execute the code by creating a <script> node, populating it with the code, and appending it to the document.
In order to simulate a true reload, p5-webeditor must clean the global scope before executing the new code. For example, if the user defines the mousePressed function and then removes it, the old mousePressed must be unset because there is nothing in the new code to overwrite the old behavior. p5-webeditor keeps a list of p5 functions that the user might define in the global scope, and sets each to undefined before overriding them with the new code. Then, setup is called in order to trigger a restart of the sketch.
The program may still fail on execution due to runtime errors not found in static analysis, like ReferenceError. p5-webeditor intercepts errors thrown by functions in p5.prototype with shims that surround the original function with a try/catch block. When one of these functions throws a runtime error, instead of crashing the browser javascript runtime the error will be caught and displayed in a UI console attached to the editor.