Overview

MyCroCloud functions let you write JavaScript handlers that run on the server in response to HTTP requests. Each function is a single handler function that receives a request object and returns a response.

function handler(request) {
  return {
    statusCode: 200,
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify({ message: 'Hello, world!' })
  };
}

How It Works

When a request matches a function route, MyCroCloud:

1. Spins up an isolated Docker container
2. Passes the HTTP request data to your handler
3. Executes your JavaScript code
4. Returns the response to the caller
5. Destroys the container

Each invocation runs in a fresh, isolated environment — there is no shared state between requests.

Runtime

Functions run on Jint, a JavaScript engine for .NET. Jint supports most of the ECMAScript 2022 specification, including:

• let, const, arrow functions, template literals
• Destructuring, spread/rest operators
• Array and Object methods (map, filter, reduce, entries, keys, values, etc.)
• JSON.parse() and JSON.stringify()
• Map, Set, WeakMap, WeakSet
• Symbol
• for...of loops, iterators
• Classes
• Optional chaining (?.) and nullish coalescing (??)
• Regular expressions

What's Not Supported

Since MyCroCloud functions use a synchronous JavaScript engine, several features commonly available in Node.js or browsers are not supported:

Feature	Why
Promise, async/await	The runtime is synchronous. fetch() is provided as a synchronous alternative.
setTimeout, setInterval	No event loop — timers are not available.
import / require	No module system. All code must be in a single handler file.
Node.js APIs (fs, path, http, crypto, etc.)	Functions run in Jint, not Node.js.
Web APIs (DOM, window, document, localStorage)	No browser environment.
Buffer	Not available. Use strings for data handling.
TextEncoder / TextDecoder	Not available.
Date timezone configuration	Date is available, but timezone behavior depends on the server.

tip

The built-in fetch() function works synchronously — no await needed. Call it like a regular function and use the result immediately.

const data = fetch('https://api.example.com/data').json();

Available APIs

MyCroCloud provides the following built-in APIs:

API	Description
fetch()	Make HTTP requests to external services (synchronous)
console	Log messages for debugging

Resource Limits

Each function invocation runs in an isolated container with the following limits:

Resource	Limit
Execution timeout	3 seconds (code execution)
Container timeout	10 seconds (configurable, includes startup)
Memory	64 MB
CPU	0.25 cores
Processes/threads	100 PIDs

Environment Variables

You can define environment variables in your app settings. They are available as a global env object:

function handler(request) {
  const apiKey = env.API_KEY;
  const res = fetch('https://api.example.com/data', {
    headers: { 'Authorization': 'Bearer ' + apiKey }
  });

  return {
    statusCode: 200,
    headers: { 'content-type': 'application/json' },
    body: res.text()
  };
}