The central job processing program used by OpenFn integration tools.

Usage no npm install needed!

<script type="module">
  import openfnCore from 'https://cdn.skypack.dev/@openfn/core';


OpenFn Core

Build Status CircleCI

Core is the central job processing program used in the OpenFn platform. It creates an isolated Node VM, passes in state and an expression, then runs the expression in this limited access Node VM.

Getting Started

It's recommended to start by getting openfn-devTools setup for a quick development environment on your machine.

After that you can use core execute to run your jobs.

Install via NPM

npm install @openfn/core

Via git

git clone git@github.com:OpenFn/core.git
cd core


Used to convert an expression into an executable script.


-l, --language    resolvable language/adaptor path                [required]
-e, --expression  target expression to execute                    [required]
-s, --state       Path to initial state file.                     [required]
-o, --output      Path to write result from expression
-t, --test        Intercepts and logs all HTTP requests to console


Use a module in the parent folder, and pick out the Adaptor member.

core execute -l ../language-http.Adaptor -e exp.js -s state.json

Use a npm installed module, and pick out the Adaptor member.

core execute -l language-http.Adaptor -e exp.js -s state.json

Using Programmatically

When creating your own runtimes, it makes more sense to call the execution code directly in NodeJS instead of via the command line.

const {
  transforms: { defaultTransforms, verify },
  sandbox: { buildSandbox, VMGlobals },
} = require('./lib');

const {
} = require('./lib/utils');

(async function () {
  const state = JSON.parse(await readFile('./test/fixtures/addState.json'));
  const code = await readFile('./test/fixtures/addExpression.js.expression');
  const Adaptor = getModule(modulePath('../language-common'));

  // Setup our initial global object, adding language packs and any other
  // objects we want on our root.
  const sandbox = buildSandbox({
    noConsole: false,
    testMode: false,
    extensions: [Adaptor],

  // Apply some transformations to the code (including a verify step) to
  // check all function calls are valid.
  const compile = new Compile(code, [
    verify({ sandbox: { ...sandbox, ...VMGlobals} }),

  if (compile.errors.length > 0) {
    throw new Error(
      compile.errors.map(err => formatCompileError(code, err)).join('\n')

  try {
    // Run the expression and get the resulting state
    const finalState = await Execute({
      expression: compile.toString(),

    writeJSON('/tmp/output.json', finalState);
  } catch (err) {

We add VMGlobals to the verify transform, and not into the sandbox that Execute uses, as VM2 provides it's own proxied copies of these functions for each invocation - but we still need the validation step to be aware that these generic functions are available


Note that only certain parts of Node are whitelisted for use in Core. These are the globals exposed by VM2 and the extensions we add for each run:

const extensions = Object.assign(
    console: argv.noConsole ? disabledConsole : console, // --nc or --noConsole
    testMode: argv.test, // --t or --test
    setTimeout, // We allow as Erlang will handle killing long-running VMs.

This means that you'll have access to whatever is exposed by the language-package (aka Adaptor), console (unless blocked by a project administrator for OpenFn Platform projects), and setTimeout. The testMode property is used to intercept HTTP requests for offline testing.

Writing language-packages

Canonical sync "operation" or "helper function" for a language-pacakge

export function sample(arg1, arg2) {
  return state => {
    state.output = arg1 + arg2;
    return state;

Canonical async "operation" or "helper function" for a language-pacakge

export function sample(arg1, arg2) {
  return state => {
    return new Promise((resolve, reject) => {
      try {
        state.output = arg1 + arg2;
      } catch (error) {

Internal notes on how execute works

(function(state) {
    alterState(() => {}),
    alterState((state) => {}), // function(state) { }
    alterState(() => {})

  (alterState(() => {}), alterState(() => {}), alterState(() => {}))
].reduce((acc, v) => {
  return v(state).then(acc)
}, new Promise);

f(state).then((state) => return state).then()