Module System

DieselEngine scripts are ES modules (ECMAScript 2023+) executed by GraalVM. They support modern JavaScript syntax including import/export, async/await, destructuring, optional chaining, and more.

Imports

Use standard ES module import syntax with relative paths and the .js extension (required):

// Import a named export
import { UserService } from '../services/UserService.js';

// Import multiple named exports
import { validate, sanitize } from '../classes/Validators.js';

// Namespace import
import * as helpers from './helpers.js';

// Default import
import config from '../config.js';

WARNING

The .js extension is required on all import paths. Extensionless imports like '../services/UserService' will fail.

Exports

Use standard export syntax:

// Named exports
export function handleRequest(context) { /* ... */ }
export class ItemService { /* ... */ }
export const API_VERSION = 2;

// Default export
export default class Config { /* ... */ }

Path Resolution

All import paths are resolved relative to the importing script's location in the virtual filesystem. There are no node_modules, no package resolution, and no path aliases.

Given this file tree:

/services/
  UserService.js
  ItemService.js
/ingresses/api/
  get-user.js

From /ingresses/api/get-user.js, you would import:

import { UserService } from '../../services/UserService.js';

How It Works Under the Hood

DieselEngine implements a custom FileSystem for GraalVM that resolves module paths against the virtual tree stored in PostgreSQL — not the host filesystem. When you write import { X } from './foo.js', the engine:

1. Resolves ./foo.js relative to the current script's parent folder
2. Looks up the resolved path in the virtual filesystem tree
3. Loads the file content from PostgreSQL
4. Evaluates it as an ES module

Supported JavaScript Features

Since DieselEngine runs on GraalVM's JS engine, you get full ECMAScript 2023+ support:

• Arrow functions, template literals, destructuring
• async/await and Promises
• class syntax with static methods
• Optional chaining (?.) and nullish coalescing (??)
• for...of, for...in, spread/rest operators
• Map, Set, WeakMap, WeakRef
• Array.prototype.at(), Object.groupBy(), etc.

INFO

There is no require(). Only ES module import/export is supported.

Top-Level Await

Top-level await is supported in scripts that run as top-level modules (on-demand, cron, startup). Ingress handlers export functions that are called synchronously by the engine.