🧰 Using the API

The API gives you finer-grained control over the CLI, allowing you to dispatch events to workers without making actual HTTP requests. This makes it great for writing tests, or advanced use cases.

​Installation

Miniflare is installed using npm:

$ npm install -D miniflare

​Usage

In all future examples, we'll assume Node.js is running in ES module mode. You can do this by setting the type field in your package.json:

package.json
{
  "type": "module"
}

To initialise Miniflare, import the Miniflare class from miniflare:

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: `
  addEventListener("fetch", (event) => {
    event.respondWith(new Response("Hello Miniflare!"));
  });
  `,
});
const res = await mf.dispatchFetch("http://localhost:8787/");
console.log(await res.text()); // Hello Miniflare!

The rest of these docs go into more detail on configuring specific features.

​String and File Scripts

Note in the above example we're specifying script as a string. We could've equally put the script in a file such as worker.js, then used the scriptPath property instead:

const mf = new Miniflare({
  scriptPath: "worker.js",
});

​Watching, Reloading and Disposing

You can watch scripts, .env, package.json and wrangler.toml files with the watch option. When this is enabled, you must dispose of the watcher when you're done with the Miniflare instance:

const mf = new Miniflare({
  watch: true,
});
// ...
await mf.dispose();

You must also dispose if you're persisting KV, cache, or Durable Object data in Redis to close opened connections.

You can also manually reload scripts (main and Durable Objects') and options (.env, package.json and wrangler.toml) with reload:

const mf = new Miniflare({ ... });
await mf.reload();

Miniflare will emit a reload event whenever it reloads too:

const mf = new Miniflare({ ... });
mf.addEventListener("reload", (event) => {
  console.log("Worker reloaded!");
});

​Updating Options and the Global Scope

You can use the setOptions method to update the options of an existing Miniflare instance. This accepts the same options object as the new Miniflare constructor, applies those options, then reloads the worker.

const mf = new Miniflare({
  script: "...",
  kvNamespaces: ["TEST_NAMESPACE"],
  bindings: { KEY: "value1" },
});

// Only updates `bindings`, leaves `script` and `kvNamespaces` alone
await mf.setOptions({
  bindings: { KEY: "value2" },
});

You can also access the global scope of the sandbox directly using the getGlobalScope method. Ideally, use should use the setOptions method when updating the environment dynamically, as Miniflare creates a new global scope each reload, so your changes will be lost:

const mf = new Miniflare({
  globals: { KEY: "value1" },
});
const globalScope = await mf.getGlobalScope();
globalScope.KEY = "value2";

​Dispatching Events

dispatchFetch and dispatchScheduled dispatch fetch and scheduled events to workers respectively:

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: `
  addEventListener("fetch", (event) => {
    event.waitUntil(Promise.resolve(event.request.url));
    event.respondWith(new Response(event.request.headers.get("X-Message")));
  });
  addEventListener("scheduled", (event) => {
    event.waitUntil(Promise.resolve(event.scheduledTime));
  });
  `,
});

const res = await mf.dispatchFetch("http://localhost:8787/", {
  headers: { "X-Message": "Hello Miniflare!" },
});
console.log(await res.text()); // Hello Miniflare!
console.log((await res.waitUntil())[0]); // http://localhost:8787/

const waitUntil = await mf.dispatchScheduled(1000);
console.log(waitUntil[0]); // 1000

See 📨 Fetch Events and ⏰ Scheduled Events for more details.

​HTTP Server

To start an HTTP server like the CLI's, use the startServer method. This returns a Node.js http.ServerOpen external link instance:

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: `
  addEventListener("fetch", (event) => {
    event.respondWith(new Response("Hello Miniflare!"));
  });
  `,
  port: 5000,
});
const server = await mf.startServer();
console.log("Listening on :5000");

You can also just create the server with createServer and start it yourself. Note that you're then responsible for setting the correct host and port:

const mf = new Miniflare({
  script: "...",
  port: 5000,
});
const server = await mf.createServer();
const { HTTPPlugin } = await mf.getPlugins();
server.listen(HTTPPlugin.port, () => {
  console.log(`Listening on :${HTTPPlugin.port}`);
});

​Request#cf Object

By default, Miniflare will fetch the Request#cf object from a trusted Cloudflare endpoint. You can disable this behaviour, using the cfFetch option:

const mf = new Miniflare({
  cfFetch: false,
});

You can also provide a custom request metadata provider, which takes the incoming Node request and may look-up information in a geo-IP database:

const mf = new Miniflare({
  async metaProvider(req) {
    return {
      forwardedProto: req.headers["X-Forwarded-Proto"],
      realIp: req.headers["X-Forwarded-For"],
      cf: {
        // Could get these from a geo-IP database
        colo: "SFO",
        country: "US",
        // ...
      },
    };
  },
});

​HTTPS Server

To start an HTTPS server instead, set the https option. To use an automatically generated self-signed certificate, set https to true. This certificate will be valid for 30 days and be cached in ./.mf/cert by default. You can customise this directory by setting https to a string path instead. The certificate will be renewed if it expires in less than 2 days:

const mf = new Miniflare({
  https: true, // Cache certificate in ./.mf/cert
  https: "./cert_cache", // Cache in ./cert_cache instead
});

To load an existing certificate from the file system:

const mf = new Miniflare({
  // These are all optional, you don't need to include them all
  httpsKeyPath: "./key.pem",
  httpsCertPath: "./cert.pem",
  httpsCaPath: "./ca.pem",
  httpsPfxPath: "./pfx.pfx",
  httpsPassphrase: "pfx passphrase",
});

To load an existing certificate from strings instead:

const mf = new Miniflare({
  // These are all optional, you don't need to include them all
  httpsKey: "-----BEGIN RSA PRIVATE KEY-----...",
  httpsCert: "-----BEGIN CERTIFICATE-----...",
  httpsCa: "...",
  httpsPfx: "...",
  httpsPassphrase: "pfx passphrase",
});

If both a string and path are specified for an option (e.g. httpsKey and httpsKeyPath), the string will be preferred.

​CRON Scheduler

To start a CRON scheduler like the CLI's, use the startScheduler method. This will dispatch scheduled events according to the specified CRON expressions:

const mf = new Miniflare({
  crons: ["30 * * * *"],
});
const scheduler = await mf.startScheduler();
// ...
// Stop dispatching events
await scheduler.dispose();

​Logging

By default, [mf:*] logs as seen in the CLI are disabled when using the API. To enable these, set the log property to an instance of the Log class. Its only parameter is a log level indicating which messages should be logged:

import { Miniflare, Log, LogLevel } from "miniflare";

const mf = new Miniflare({
  scriptPath: "worker.js",
  log: new Log(LogLevel.DEBUG), // Enable --debug messages
});

​Arbitrary Globals

The globals property can be used to inject arbitrary objects into the global scope of the sandbox. This can be very useful for testing:

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: `
  addEventListener("fetch", (event) => {
    event.respondWith(new Response(greet("Miniflare")));
  });
  `,
  globals: {
    greet: (name) => `Hello ${name}!`,
  },
});
const res = await mf.dispatchFetch("http://localhost:8787/");
console.log(await res.text()); // Hello Miniflare!

​Reference

import { Miniflare, Log, LogLevel } from "miniflare";

const mf = new Miniflare({
  // All options are optional, but one of script or scriptPath is required

  log: new Log(LogLevel.INFO), // Logger Miniflare uses for debugging
  sourceMap: true, // Enable source map support globally

  script: `export default {
    async fetch(request, env, ctx) {
      return new Response("Hello Miniflare!");
    }
  }`,
  scriptPath: "./index.mjs",

  wranglerConfigPath: true, // Load configuration from wrangler.toml
  wranglerConfigPath: "./wrangler.custom.toml", // ...or custom wrangler.toml path

  wranglerConfigEnv: "dev", // Environment in wrangler.toml to use

  packagePath: true, // Load script from package.json
  packagePath: "./package.custom.json", // ...or custom package.json path

  modules: true, // Enable modules
  modulesRules: [
    // Modules import rule
    { type: "ESModule", include: ["**/*.js"], fallthrough: true },
    { type: "Text", include: ["**/*.text"] },
  ],
  compatibilityDate: "2021-11-23", // Opt into backwards-incompatible changes from
  compatibilityFlags: ["formdata_parser_supports_files"], // Control specific backwards-incompatible changes
  upstream: "https://miniflare.dev", // URL of upstream origin
  watch: true, // Watch files for changes
  mounts: {
    // Mount additional named workers
    api: "./api",
    site: {
      rootPath: "./site", // Path to resolve files relative to
      scriptPath: "./index.js", // Resolved as ./site/index.js
      sitePath: "./public", // Resolved as ./site/public
      routes: ["*site.mf/*"], // Route requests matching *site.mf/* to this worker
    },
  },
  name: "worker", // Name of service
  routes: ["*site.mf/parent"], // Route requests matching *site.mf/parent to parent over mounts

  logUnhandledRejections: true, // Log unhandled promise rejections instead of crashing

  globalAsyncIO: true, // Allow async I/O outside handlers
  globalTimers: true, // Allow setting timers outside handlers
  globalRandom: true, // Allow secure random generation outside handlers

  acutalTime: true, // Always return current time from `Date.now()`/`new Date()`

  inaccurateCpu: true, // Log experimental, highly-inaccurate CPU time measurements with each request

  host: "127.0.0.1", // Host for HTTP(S) server to listen on
  port: 8787, // Port for HTTP(S) server to listen on
  https: true, // Enable self-signed HTTPS (with optional cert path)
  httpsKey: "-----BEGIN RSA PRIVATE KEY-----...",
  httpsKeyPath: "./key.pem", // Path to PEM SSL key
  httpsCert: "-----BEGIN CERTIFICATE-----...",
  httpsCertPath: "./cert.pem", // Path to PEM SSL cert chain
  httpsCa: "...",
  httpsCaPath: "./ca.pem", // Path to SSL trusted CA certs
  httpsPfx: "...",
  httpsPfxPath: "./pfx.pfx", // Path to PFX/PKCS12 SSL key/cert chain
  httpsPassphrase: "pfx passphrase", // Passphrase to decrypt SSL files
  cfFetch: "./node_modules/.mf/cf.json", // Path for cached Request cf object from Cloudflare
  async metaProvider(req) {
    // Custom request metadata provider taking Node `http.IncomingMessage`
    return {
      forwardedProto: req.headers["X-Forwarded-Proto"],
      realIp: req.headers["X-Forwarded-For"],
      cf: {
        colo: "SFO",
        country: "US",
        // ...
      },
    };
  },
  liveReload: true, // Reload HTML pages whenever worker is reloaded

  crons: ["30 * * * *"], // CRON expression for triggering scheduled events

  buildCommand: "npm run build", // Command to build project
  buildBasePath: "./build", // Working directory for build command
  buildWatchPaths: ["./src"], // Directory to watch for rebuilding on changes

  kvNamespaces: ["TEST_NAMESPACE"], // KV namespace to bind
  kvPersist: "./kv-data", // Persist KV data (to optional path)

  r2Buckets: ["BUCKET"], // R2 bucket to bind
  r2Persist: "./r2-data", // Persist R2 data (to optional path)

  durableObjects: {
    // Durable Object to bind
    TEST_OBJECT: "TestObject", // className
    API_OBJECT: { className: "ApiObject", scriptName: "api" },
  },
  durableObjectsPersist: "./durable-objects-data", // Persist Durable Object data (to optional path)
  durableObjectsAlarms: false, // Enable default/named Durable Object alarms (enabled by default)

  cache: false, // Enable default/named caches (enabled by default)
  cachePersist: "./cache-data", // Persist cached data (to optional path)
  cacheWarnUsage: true, // Warn on cache usage, for workers.dev subdomains

  sitePath: "./site", // Path to serve Workers Site files from
  siteInclude: ["**/*.html", "**/*.css", "**/*.js"], // Glob pattern of site files to serve
  siteExclude: ["node_modules"], // Glob pattern of site files not to serve

  envPath: true, // Load environment variables from .env
  envPath: "./env.custom", // ...or custom .env path

  bindings: { SECRET: "sssh" }, // Binds variable/secret to environment
  globals: { LOG: () => console.log("magic") }, // Binds variable/secret to global scope
  wasmBindings: { ADD_MODULE: "./add.wasm" }, // WASM module to bind
  textBlobBindings: { TEXT: "./text.txt" }, // Text blob to bind
  dataBlobBindings: { DATA: "./data.bin" }, // Data blob to bind
});

await mf.reload(); // Reload scripts and configuration files

await mf.setOptions({ kvNamespaces: ["TEST_NAMESPACE2"] }); // Apply options and reload

const globalScope = await mf.getGlobalScope(); // Get sandbox's global scope
const bindings = await mf.getBindings(); // Get bindings (KV/Durable Object namespaces, variables, etc)

const exports = await mf.getModuleExports(); // Get exports from entry module

const mount = await mf.getMount("api"); // Get mounted MiniflareCore instance
await mount.getBindings();

// Dispatch "fetch" event to worker
const res = await mf.dispatchFetch("http://localhost:8787/", {
  headers: { Authorization: "Bearer ..." },
});
const text = await res.text();
const resWaitUntil = await res.waitUntil(); // Get `waitUntil`ed promises

// Dispatch "scheduled" event to worker
const waitUntil = await mf.dispatchScheduled(Date.now(), "30 * * * *");

const TEST_NAMESPACE = await mf.getKVNamespace("TEST_NAMESPACE");

const BUCKET = await mf.getR2Bucket("BUCKET");

const caches = await mf.getCaches(); // Get global `CacheStorage` instance
const defaultCache = caches.default;
const namedCache = await caches.open("name");

// Get Durable Object namespace and storage for ID
const TEST_OBJECT = await mf.getDurableObjectNamespace("TEST_OBJECT");
const id = TEST_OBJECT.newUniqueId();
const storage = await mf.getDurableObjectStorage(id);

const server = await mf.createServer(); // Create http.Server instance
server.listen(8787, () => {});

const server2 = await mf.startServer(); // Create and start http.Server instance
server2.close();

const scheduler = await mf.startScheduler(); // Start CRON scheduler
await scheduler.dispose();

await mf.dispose(); // Cleanup storage database connections and watcher