polyscript

Polyscript

PyScript single core to rule them all

Terminology

This section goal is to avoid confusion around topics discussed in this document, describing each term as exhaustively as possible.

Interpreter

Also commonly referred as runtime or engine, we consider an interpreter any “piece of software” able to parse, understand, and ultimately execute, a Programming Language through this project.

We also explicitly use that “piece of software” as the interpreter name it refers to. We currently bundle references to the following interpreters:

  • pyodide is the name of the interpreter that runs likely the most complete version of latest Python, enabling dozen official modules at run time, also offering a great JS integration in its core
  • micropython is the name of the interpreter that runs a small subset of the Python standard library and is optimized to run in constrained environments such as Mobile phones, or even Desktop, thanks to its tiny size and an extremely fast bootstrap
  • ruby-wasm-wasi is the name of the (currently experimental) interpreter that adds Ruby to the list of programming languages currently supported
  • wasmoon is the name of the interpreter that runs Lua on the browser and that, among the previous two interpreters, is fully compatible with all core features
  • webr is the name of the (currently experimental) interpreter that adds R to the list of programming languages currently supported

<script> tags specify which interpreter to use via the type attribute. This is typically the full name of the interpreter:

<script type="pyodide">
    import sys
    print(sys.version)
</script>

<script type="micropython">
    import sys
    print(sys.version)
</script>

<script type="ruby-wasm-wasi">
    print "ruby #{ RUBY_VERSION }"
</script>

<script type="wasmoon">
    print(_VERSION)
</script>

<script type="webr">
    print(R.version.string)
</script>

ℹ️ - Please note we decided on purpose to not use the generic programming language name instead of its interpreter project name to avoid being too exclusive for alternative projects that would like to target that very same Programming Language (i.e. note pyodide & micropython not using python indeed as interpreter name).

Custom values for the type attribute can also be created which alias (and potential build on top of) existing interpreter types. We include <script type="py"> (and its <py-script> custom element counter-part) which use the Pyodide interpreter while extending its behavior in specific ways familiar to existing PyScript users (the <py-config> tag, <py-repl>, etc).

Target

When it comes to strings or attributes, we consider the target any valid element’s id on the page or, in most cases, any valid CSS selector.

<!-- ℹ️ - requires py-script custom type -->
<script type="py">
    # target here is a string
    display('Hello PyScript', target='output')
</script>
<div id="output">
    <!-- will show "Hello PyScript" once the script executes -->
</div>

When it comes to the property or field attached to a <script> element though, that id or selector would already be resolved, so that such field would always point at the very same related element.

<script type="micropython" target="output">
    from js import document
    document.currentScript.target.textContent = "Hello";
</script>
<div id="output">
    <!-- will show "Hello" once the script executes -->
</div>

ℹ️ - Please note that if no target attribute is specified, the script will automatically create a “companion element” when the target property/field is accessed for the very first time:

<script type="micropython">
    from js import document

    # will create a <script-micropython> element appended
    # right after the currently executing script
    document.currentScript.target.textContent = "Hello";
</script>
<!--
    created during previous code execution

    <script-micropython>Hello</script-micropython>
-->
Env

ℹ️ - This is an advanced feature that is worth describing but usually it is not needed for most common use cases.

Mostly due its terseness that plays nicely as attribute’s suffix, among its commonly understood meaning, we consider an env an identifier that guarantee the used interpreter would always be the same and no other interpreters, even if they point at very same project, could interfere with globals, behavior, or what’s not.

In few words, every single env would spawn a new interpreter dedicated to such env, and global variables defined elsewhere will not affect this “environment” and vice-versa, an env cannot dictate what will happen to other interpreters.

<!-- default env per each interpreter -->
<script type="micropython">
    shared = True
</script>
<script type="micropython">
    # prints True - shared is global
    print(shared)
</script>

<!-- dedicated interpreter -->
<script type="micropython" env="my-project-env">
    # throws an error - shared doesn't exist
    print(shared)
</script>

ℹ️ - Please note if the interpreter takes 1 second to bootstrap, multiple environments will take that second multiplied by the number of different environments, which is why this feature is considered for advanced use cases only and it should be discouraged as generic practice.

Bootstrapping core

In order to have anything working at all in our pages, we need to at least bootstrap polyscript functionalities, otherwise all examples and scripts mentioned in this document would just sit there … sadly ignored by every browser:

<!doctype html>
<html>
    <head>
        <!-- this is a way to automatically bootstrap polyscript -->
        <script type="module" src="https://cdn.jsdelivr.net/npm/polyscript"></script>
    </head>
    <body>
        <script type="micropython">
            from js import document
            document.body.textContent = 'polyscript'
        </script>
    </body>
</html>

As core exposes some utility/API, using the following method would also work:

<script type="module">
    import {
        define,      // define a custom type="..."
        whenDefined, // wait for a custom type to be defined
        XWorker      // allows JS <-> Interpreter communication
    } from 'https://cdn.jsdelivr.net/npm/polyscript';
</script>

Please keep reading this document to understand how to use those utilities or how to have other Pogramming Languages enabled in your page via <script> elements.

How Scripts Work

The <script> element has at least these extremely important peculiarities compared to any other element defined by the HTML Standard:

The long story short is that any <script type="non-standard-type"> has zero issues with any browser of choice, but it’s true that using some specific custom type might lead to future issues in case that type could have some special meaning for the future of the Web.

We encourage everyone to be careful when using this core API as we definitively don’t want to clash or conflict, by any mean, with what the Web might need or offer in the near to far future, but we’re also confident so far our current types are more than safe.

Script Attributes

name example behavior
async <script type="pyodide" async> The code is evaluated via runAsync utility where, if the interpreter allows it, top level await would be possible, among other PL specific asynchronous features.
config <script type="pyodide" config="./cfg.toml"> The interpreter will load and parse the JSON or TOML file to configure itself. Please see currently supported config values as this is currently based on <py-config> features.
env <script type="pyodide" env="brand"> Create, if not known yet, a dedicated environment for the specified type. Please read the Terminology env dedicated details to know more.
src <script type="pyodide" src="./app.py"> Fetch code from the specified src file, overriding or ignoring the content of the <script> itself, if any.
target <script type="pyodide" target="outcome"> Describe as id or CSS selector the default target to use as document.currentScript.target field. Please read the Terminology target dedicated details to know more.
type <script type="micropython"> Define the interpreter to use with this script. Please read the Terminology interpreter dedicated details to know more.
version <script type="pyodide" version="0.23.2"> Allow the usage of a specific version where, if numeric, must be available through the project CDN used by core but if specified as fully qualified URL, allows usage of any interpreter’s version: <script type="pyodide" version="http://localhost:8080/pyodide.local.mjs">
worker <script type="pyodide" worker="./file.py"> Bootstraps an interpreter only within a worker, allowing config and version attributes too, also attaching an xworker property/field directly to the script tag on the main page. Please note the interpreter will not be available on the main thread when this attribute is used.
service-worker <script type="pyodide" service-worker="../sw.js" worker> Eventually does fallback to a Service Worker able to enable also synchronous interactions to grant access to the xworker.window proxy.

Script Features

These are all special, script related features, offered by polyscript out of the box.

document.currentScript

No matter the interpreter of choice, if there is any way to reach the document from such interpreter, its currentScript will point at the exact/very-same script that is currently executing the code, even if its async attribute is used, mimicking what the standard document.currentScript offers already, and in an unobtrusive way for the rest of the page, as this property only exists for synchronous and blocking scripts that are running, hence never interfering with this core logic or vice-versa.

<script type="micropython" id="my-target">
    from js import document

    # explicitly grab the current script as target
    my_target = document.getElementById('my-target')

    # verify it is the exact same node with same id
    print(document.currentScript.id == my_target.id)
</script>

Not only this is helpful to crawl the surrounding DOM or HTML, every script will also have a target property that will point either to the element reachable through the target attribute, or it lazily creates once a companion element that will be appended right after the currently executing script.

Please read the Terminology target dedicated details to know more.

XWorker

With or without access to the document, every (non experimental) interpreter will have defined, either at the global level or after an import (i.e.from polyscript import XWorker in Python case), a reference to the XWorker “class” (it’s just a function!), which goal is to enable off-loading heavy operations on a worker, without blocking the main / UI thread (the current page) and allowing such worker to even reach the document or anything else available on the very same main / UI thread.

<script type="micropython">
    from polyscript import XWorker
    print(XWorker != None)
</script>

Please read the XWorker dedicated section to know more.

Extra config features

It is possible to land in either the main world or the worker one native JS modules (aka: ESM).

In polyscript, this is possible by defining one or more [js_modules.X] fields in the config, where X is either main or worker:

All registeed modules can be then imported as such:

# just import js_modules and reach names after
from polyscript import js_modules
js_modules.my_module.util()

# import directly and reach names after
from polyscript.js_modules import my_module
my_module.util()

# import deeply up to the module exports
from polyscript.js_modules.my_module import util
util()

# import default or other fields with aliases
from polyscript.js_modules.other import defalut as fn
fn()

js_modules config example

TOML

[js_modules.main]
# this modules work best on main
"https://cdn.jsdelivr.net/npm/leaflet@1.9.4/dist/leaflet-src.esm.js" = "leaflet"
"https://cdn.jsdelivr.net/npm/leaflet@1.9.4/dist/leaflet.css" = "leaflet" # CSS
# this works in both main and worker
"https://cdn.jsdelivr.net/npm/html-escaper" = "html_escaper"

[js_modules.worker]
# this works out of the box in a worker too
"https://cdn.jsdelivr.net/npm/html-escaper" = "html_escaper"
# this works only in a worker
"https://cdn.jsdelivr.net/npm/worker-only" = "worker_only"

JSON

{
  "js_modules": {
    "main": {
      "https://cdn.jsdelivr.net/npm/leaflet@1.9.4/dist/leaflet-src.esm.js": "leaflet",
      "https://cdn.jsdelivr.net/npm/leaflet@1.9.4/dist/leaflet.css": "leaflet",
      "https://cdn.jsdelivr.net/npm/html-escaper": "html_escaper"
    },
    "worker": {
      "https://cdn.jsdelivr.net/npm/html-escaper": "html_escaper",
      "https://cdn.jsdelivr.net/npm/worker-only": "worker_only"
    }
  }
}

Python

<!-- main case -->
<script type="pyodide" config="./that.toml">
  # these both works
  from polyscript.js_modules import leaflet as L
  from polyscript.js_modules import html_escaper

  # this fails as it's not reachable in main
  from polyscript.js_modules import worker_only
</script>

<!-- worker case -->
<script type="pyodide" config="./that.toml" worker>
  # these works by proxying the main module and landing
  # on main only when accessed, never before
  # the CSS file also lands automatically on demand
  from polyscript.js_modules import leaflet as L

  # this works out of the box in the worker
  from polyscript.js_modules import html_escaper

  # this works only in a worker 👍
  from polyscript.js_modules import worker_only
</script>

.tar.gz and .zip files

If the [files] entry in the config contains a xxxxx.tar.gz or xxxxx.zip source, and it’s destination / target is a folder with a star, such as /* for root or ./dest/* for local folders, both Pyodide and MicroPython runtimes will be able to extract that compressed archive automatically into the Virtual File System and at exactly that location.

This feature is hence available on PyScript too.

The polyscript Module

The module is registered within the interpreter as JS module and it offers various helpers or utilities accordingly if it’s running on the main thread or the worker one.

Main exports

name example description
XWorker from polyscript import XWorker described in the XWorker part.
config from polyscript import config custom only: the used config as object literal
currentScript from polyscript import currentScript it’s an explicit, always correct, reference to the current node running the generic script code.
js_modules from polyscript import js_modules described in the Extra config Features part.
lazy_py_modules from polyscript import lazy_py_modules allows, only in Python related interpreters, and without needing static config entries, to import lazily any available module.
storage from polyscript import storage a utility to instantiate a named idb-map that can be consumed synchronously.
JSON from polyscript import JSON a utility to stringify/parse more complex or recursive data via @ungap/structured-clone/json.

lazy_py_modules

<script type="pyodide" async>
  from polyscript import lazy_py_modules

  matplotlib, regex, = await lazy_py_modules("matplotlib", "regex")

  print(matplotlib, regex)
</script>

storage

<script type="micropython" async>
  from polyscript import storage

  # await its loading
  map = await storage("my-user-persistent-storage")

  # just use it synchronously
  map.set("key", "value")
  print(map.get("key"))

  # after set, delete, or clear
  # it is possible to sync operations
  await map.sync()
</script>

Worker exports

name example description
xworker from polyscript import xworker described in the XWorker part.
config from polyscript import config custom only: the used config as object literal
currentScript from polyscript import currentScript it’s an explicit, always correct, reference to the current node running the generic script code via a worker.
js_modules from polyscript import js_modules described in the Extra config Features part.
target from polyscript import target returns the element referenced by the target attribute, if any, or create a target node to display output when this has not been provided.

How Events Work

The event should contain the interpreter or custom type prefix, followed by the event type it’d like to handle.

<script type="micropython">
    def print_type(event):
        print(event.type)
</script>
<button micropython-click="print_type">
    print type
</button>

Differently from Web inline events, there’s no code evaluation at all within the attribute: it’s just a globally available name that will receive the current event and nothing else.

The type-env attribute

Just as the env attribute on a <script> tag specifies a specific instance of an interpreter to use to run code, it is possible to use the [type]-env attribute to specify which instance of an interpreter or custom type should be used to run event code:

<script type="micropython">
    def log(event):
        print(1)
</script>
<!-- note the env value -->
<script type="micropython" env="two">
    # the button will log 2
    def log(event):
        print(2)
</script>
<!-- note the micropython-env value -->
<button
    micropython-env="two"
    micropython-click="log"
>
    log
</button>

As mentioned before, this will work with py-env too, or any custom type defined out there.

XWorker

Whenever computing relatively expensive stuff, such as a matplot image, or literally anything else that would take more than let’s say 100ms to answer, running your interpreter of choice within a Web Worker is likely desirable, so that the main / UI thread won’t block users’ actions, listeners, or any other computation going on in these days highly dynamic pages.

polyscript adds a functionality called XWorker to all of the interpreters it offers, which works in each language the way Worker does in JavaScript.

In each Interpreter, XWorker is either global reference or an import (i.e.from polyscript import XWorker in Python case) module’s utility, with a counter xworker (lower case) global reference, or an import (i.e.from polyscript import xworker in Python case) module’s utility, within the worker code.

In short, the XWorker utility is to help, without much thinking, to run any desired interpreter out of a Worker, enabling extra features on the worker’s code side.

Enabling XWorker

We use the latest Web technologies to allow fast, non-blocking, yet synchronous like, operations from any non-experimental interpreter’s worker, and the standard requires some special header to enable such technologies and, most importantly, the SharedArrayBuffer.

There is an exhaustive section around this topic but the TL;DR version is:

There are alternative ways to enable these headers for your site or local host, and this script is just one of these, one that works with most free-hosting websites too.

XWorker options

Before showing any example, it’s important to understand how the offered API differs from Web standard workers:

name example behavior
async XWorker('./file.py', async=True) The worker code is evaluated via runAsync utility where, if the interpreter allows it, top level await would be possible, among other PL specific asynchronous features.
config XWorker('./file.py', config='./cfg.toml') The worker will either use the config object as it is or load and parse its referencing JSON or TOML file, or syntax, to configure itself. Please see currently supported config values as this is currently based on <py-config> features.
type XWorker('./file.py', type='pyodide') Define the interpreter to use with this worker which is, by default, the same one used within the running code. Please read the Terminology interpreter dedicated details to know more.
version XWorker('./file.py', type='pyodide', version='0.23.2') Allow the usage of a specific version where, if numeric, must be available through the project CDN used by core but if specified as fully qualified URL, allows usage of any interpreter’s version: <script type="pyodide" version="http://localhost:8080/pyodide.local.mjs">
serviceWorker XWorker('./file.py', type='pyodide', serviceWorker='../sw.js') When the server cannot enable SharedArrayBuffer it is still possible to fallback to a Service Worker file based orchestration provided by mini-coi, sabayon or others. Please note that this string must point to a file in the current server.

The returning JS reference to any XWorker(...) call is literally a Worker instance that, among its default API, have the extra following feature:

name example behavior
sync sync = XWorker('./file.py').sync Allows exposure of callbacks that can be run synchronously from the worker file, even if the defined callback is asynchronous. This property is also available in the xworker reference. 
from polyscript import XWorker

sync = XWorker('./file.py').sync

def from_main(some, value):
    # return something interesting from main
    # or do anything else
    print(some)
    print(value)

sync.from_main = from_main

In the xworker counter part:

from polyscript import xworker

# will log 1 and "two" in default stdout console
xworker.sync.from_main(1, "two")

The xworker reference

The content of the file used to initialize any XWorker on the main thread can always reach the xworker counter part as globally available or as import (i.e.from polyscript import xworker in Python case) module’s utility.

Within a Worker execution context, the xworker exposes the following features:

name example behavior
polyfill xworker.polyfill Returns true if sabayon polyfill is used behind the scene.
sync xworker.sync.from_main(1, "two") Executes the exposed from_main function in the main thread. Returns synchronously its result when SharedArrayBuffer can work synchronously. Returns asynchronously otherwise exposed callbacsk from the main thread.
window xworker.window.document.title = 'Worker' Differently from pyodide or micropython import js, this field allows every single possible operation directly in the main thread when that is possible (SharedArrayBuffer either available or polyfilled for sync operations too). It does not refer to the local js environment the interpreter might have decided to expose, it is a proxy to handle otherwise impossible operations in the main thread, such as manipulating the DOM, reading localStorage otherwise not available in workers, change location or anything else usually possible to do in the main thread.
isWindowProxy xworker.isWindowProxy(ref) Advanced - Allows introspection of JS references, helping differentiating between local worker references, and main thread global JS references. This is valid both for non primitive objects (array, dictionaries) as well as functions, as functions are also enabled via xworker.window in both ways: we can add a listener from the worker or invoke a function in the main. Please note that functions passed to the main thread will always be invoked asynchronously. 
from polyscript import xworker

print(xworker.window.document.title)

xworker.window.document.body.append("Hello Main Thread")

xworker.window.setTimeout(print, 100, "timers too")

ℹ️ - Please note that even if non blocking, if too many operations are orchestrated from a worker, instead of the main thread, the overall performance might still be slower due the communication channel and all the primitives involved in the synchronization process. Feel free to use the window feature as a great enabler for unthinkable or quick solutions but keep in mind it is still an indirection.

Just the XWorker

If you only need the XWorker class from JS, or the internal Hook class to define custom worker (only) hooks remotely, you can import { XWorker, Hook } from 'polyscript/xworker' and see how far you can go with it.

The sync utility

This helper does not interfere with the global context but it still ensure a function can be exposed form main and be used from thread and/or vice-versa.

# main
from polyscript import XWorker

def alert_user(message):
    import js
    js.alert(message)

w = XWorker('./file.py')
# expose the function to the thread
w.sync.alert_user = alert_user


# thread
from polyscript import xworker

if condition == None:
    xworker.sync.alert_user('something wrong!')

Custom Scripts

With polyscript it is possible to extend any interpreter, allowing users or contributors to define their own (optional) type for the <script> they would like to augment with goodness or extra simplicity.

The core module itself exposes two methods to do so:

name example behavior
define define('mpy', options) Register once a <script type="mpy">, if it’s a string, and a counter <mpy-script> selector that will bootstrap and handle all nodes in the page that match such selectors. If the type is either null or undefined, no type will exist but the interpreter will be bootstrapped anyway, hence available once options.hooks.main.onReady(wrap) is invoked (without any element reference). The available options are described after this table.
whenDefined whenDefined('mpy') Return a promise that will be resolved once the custom mpy script will be available, returning an interpreter wrapper once it will be fully ready. 
import { define, whenDefined } from 'polyscript';

define('mpy', {
    interpreter: 'micropython',
    hooks: {
      main: {
        onReady(wrap, element) {
          console.log('here we go main!');
        }
      },
      worker: {
        onReady(wrap, xworker) {
          console.log('here we go worker!');
        }
      }
    }
    // the rest of the custom type options
});

// an "mpy" dependent plugin for the "mpy" custom type
whenDefined("mpy").then(interpreterWrapper => {
    // define or perform any task via the wrapper
})

Custom Scripts Options

Advanced - Even if we strive to provide the easiest way for anyone to use core interpreters and features, the life cycle of a custom script might require any hook we also use internally to make <script type="py"> possible, which is why this list is quite long, but hopefully exhaustive, and it covers pretty much everything we do internally as well.

The list of options’ fields is described as such and all of these are optional while defining a custom type:

name example behavior
interpreter {interpreter: 'pyodide'} Specifies the interpreter to use, such as pyodide, micropython, wasmoon or others.
config {config: 'type.toml'} {config: {}} Ensure such config is already parsed and available, if not already passed as object, for every custom type that execute code.
configURL {configURL: '/absolute/url/config.json'} If the passed config is an already resolved object, this field is neded to help resolving files in fetch or packages or others.
version {version: '0.23.2'} Allow the usage of a specific version of an interpreter, same way version attribute works with <script> elements.
env {env: 'my-project'} Guarantee same environment for every custom type, avoiding conflicts with any other possible default or custom environment.
onerror (error, element) => { throw error; } Allows custom types to intercept early errors possibly happened while bootstrapping elements.
hooks {hooks: {main: {}, worker: {}}} Allows custom types to hook logic around every main thread or worker tag via defined hooks.

Hooks

Every special script or tag inevitably passes through some main or worker thread related tasks.

In both worlds, the exact sequence of steps around code execution is the following:

As most interpreters can run their code either synchronously or asynchronously, the very same sequence is guaranteed to run in order in both cases, and the difference is only around the naming convention.

Main Hooks

When it comes to main hooks all callbacks will receive a wrapper of the interpreter with its utilities, see the further section to know more, plus the element on the page that is going to execute its related code, being this a custom script/type or a custom tag.

This is the list of all possible, yet optional hooks, a custom type can define for main:

name example behavior
onReady onReady(wrap:Wrap, el:Element) {} If defined, it is invoked before any other hook to signal that the element is going to execute the code. For custom scripts, this hook is in charge of eventually running the content of the script, anyway it prefers to do so.
onBeforeRun onBeforeRun(wrap:Wrap, el:Element) {} If defined, it is invoked before any other hook to signal that the element is going to execute the code.
onBeforeRunAsync onBeforeRunAsync(wrap:Wrap, el:Element) {} Same as onBeforeRun except it’s the one used whenever the script is async.
codeBeforeRun codeBeforeRun: () => 'print("before")' If defined, prepend some code to evaluate right before the rest of the code gets executed.
codeBeforeRunAsync codeBeforeRunAsync: () => 'print("before")' Same as codeBeforeRun except it’s the one used whenever the script is async.
codeAfterRun codeAfterRun: () => 'print("after")' If defined, append some code to evaluate right after the rest of the code already executed.
codeAfterRunAsync codeAfterRunAsync: () => 'print("after")' Same as codeAfterRun except it’s the one used whenever the script is async.
onAfterRun onAfterRun(wrap:Wrap, el:Element) {} If defined, it is invoked after the foreign code has been executed already.
onAfterRunAsync onAfterRunAsync(wrap:Wrap, el:Element) {} Same as onAfterRun except it’s the one used whenever the script is async.
onWorker onWorker(wrap = null, xworker) {} If defined, whenever a script or tag with a worker attribute is processed it gets triggered on the main thread, to allow to expose possible xworker features before the code gets executed within the worker thread. The wrap reference is most of the time null unless an explicit XWorker call has been initialized manually and/or there is an interpreter on the main thread (very advanced use case). Please note this is the only hook that doesn’t exist in the worker counter list of hooks.

Worker Hooks

When it comes to worker hooks, all non code related callbacks must be serializable, meaning that callbacks cannot use any outer scope reference, as these are forwarded as strings, hence evaluated after in the worker, to survive the main <-> worker postMessage dance.

Here an example of what works and what doesn’t:

// this works 👍
define('pl', {
  interpreter: 'programming-lang',
  hooks: {
    worker: {
      onReady() {
        // NOT suggested, just as example!
        if (!('i' in globalThis))
          globalThis.i = 0;
        console.log(++i);
      }
    }
  }
});

// this DOES NOT WORK ⚠️
let i = 0;
define('pl', {
  interpreter: 'programming-lang',
  hooks: {
    worker: {
      onReady() {
        // that outer-scope `i` is nowhere understood
        // whenever this code executes in the worker
        // as this function gets stringified and re-evaluated
        console.log(++i);
      }
    }
  }
});

At the same time, as the worker doesn’t have any element strictly related, as workers can be created also procedurally, the second argument won’t be an element but the related xworker that is driving the logic.

As summary, this is the list of all possible, yet optional hooks, a custom type can define for worker:

name example behavior
onReady onReady(wrap:Wrap, xw:XWorker) {} If defined, it is invoked before any other hook to signal that the xworker is going to execute the code. Differently from main, the code here is already known so all other operations will be performed automatically.
onBeforeRun onBeforeRun(wrap:Wrap, xw:XWorker) {} If defined, it is invoked before any other hook to signal that the xworker is going to execute the code.
onBeforeRunAsync onBeforeRunAsync(wrap:Wrap, xw:XWorker) {} Same as onBeforeRun except it’s the one used whenever the worker script is async.
codeBeforeRun codeBeforeRun: () => 'print("before")' If defined, prepend some code to evaluate right before the rest of the code gets executed.
codeBeforeRunAsync codeBeforeRunAsync: () => 'print("before")' Same as codeBeforeRun except it’s the one used whenever the worker script is async.
codeAfterRun codeAfterRun: () => 'print("after")' If defined, append some code to evaluate right after the rest of the code already executed.
codeAfterRunAsync codeAfterRunAsync: () => 'print("after")' Same as codeAfterRun except it’s the one used whenever the worker script is async.
onAfterRun onAfterRun(wrap:Wrap, xw:XWorker) {} If defined, it is invoked after the foreign code has been executed already.
onAfterRunAsync onAfterRunAsync(wrap:Wrap, xw:XWorker) {} Same as onAfterRun except it’s the one used whenever the worker script is async.

Custom Scripts Wrappers

Almost every interpreter has its own way of doing the same thing needed for most common use cases, and with this in mind we abstracted most operations to allow a terser core for anyone to consume, granting that its functionalities are the same, no matter which interpreter one prefers.

There are also cases that are not tackled directly in core, but necessary to anyone trying to extend core as it is, so that some helper felt necessary to enable users and contributors as much as they want.

In few words, while every interpreter is literally passed along to unlock its potentials 100%, the most common details or operations we need in core are:

name example behavior
type wrap.type Return the current type (interpreter or custom type) used in the current code execution.
interpreter wrap.interpreter Return the interpreter AS-IS after being bootstrapped by the desired config.
XWorker wrap.XWorker Refer to the XWorker class available to the main thread code while executing.
io wrap.io Allow to lazily define different stdout or stderr via the running interpreter. This io field can be lazily defined and restored back for any element currently running the code.
config wrap.config It is the resolved JSON config and it is an own clone per each element running the code, usable also as “state” reference for the specific element, as changing it at run time will never affect any other element.
run wrap.run(code) It abstracts away the need to know the exact method name used to run code synchronously, whenever the interpreter allows such operation, facilitating future migrations from an interpreter to another.
runAsync wrap.runAsync(code) It abstracts away the need to know the exact method name used to run code asynchronously, whenever the interpreter allows such operation, facilitating future migrations from an interpreter to another.
runEvent wrap.runEvent(code, event) It abstracts away the need to know how an interpreter retrieves paths to execute an event handler.

This is the wrap mentioned with most hooks and initializers previously described, and we’re more than happy to learn if we are not passing along some extra helper.

The io helper

// change the default stdout while running code
wrap.io.stdout = (message) => {
  console.log("🌑", wrap.type, message);
};

// change the default stderr while running code
wrap.io.stderr = (message) => {
  console.error("🌑", wrap.type, message);
};

Ready Event

Whenever a non-custom script is going to run some code, or whenever any worker is going to run its own code, a type:ready event is dispatched through the element that is currently executing the code.

The CustomEvent dispatched in either cases contains a target which refers to the element that is running code and a detail.worker boolean value that is true if such event came from a worker instead of the main thread.

The worker detail is essential to know if an xworker property is attached so that it’s also easy to pollute its sync proxy utility.

Done Event

Whenever a non-custom script is going to run some code, or whenever any worker is going to run its own code, a type:done event is dispatched through the element after its code has fully executed.

Custom Types on Main

The reason this event is not automatically dispatched on custom type elements or scripts is that these will have their own options.hooks.main.onReady hook to eventually do more before desiring, or needing, to notify the “readiness” of such custom element and, in case of wanting the event to happen, this is the tiny boilerplate needed to simulate otherwise non-custom type events:

// note: type === 'py' or the defined type
element.dispatchEvent(
  new CustomEvent(`${type}:ready`, {
    bubbles: true,
    detail: { worker: false },
  })
);

In the worker case, because the orchestration is inevitably coupled with this module, the custom type will be dispatched out of the blue to help extensions on op of this module to work best.

Explicit Worker: No Event

Please note that if a worker is created explicitly, there won’t be any element, script, or generic tag/node associated to it, so that no event will be triggered as there is no target for it. However, it’s always possible to attach sync utilities to such explicit worker, so this should never be a real-world concern or blocker.

Examples

Interpreter Features

name run runAsync runEvent registerJSModule writeFile transform
pyodide • • • • • •
micropython • • • • • •
ruby-wasm-wasi • • • !    
wasmoon • • • ! •  
webr r • re      
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