---
title: Fetch Events
description: Dispatch and test HTTP fetch events in Miniflare for Cloudflare Workers.
image: https://developers.cloudflare.com/dev-products-preview.png
---

> Documentation Index  
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# Fetch Events

* [FetchEvent Reference](https://developers.cloudflare.com/workers/runtime-apis/handlers/fetch/)

## HTTP Requests

Whenever an HTTP request is made, a `Request` object is dispatched to your worker, then the generated `Response` is returned. The `Request` object will include a [cf object](https://developers.cloudflare.com/workers/runtime-apis/request#incomingrequestcfproperties). Miniflare will log the method, path, status, and the time it took to respond.

If the Worker throws an error whilst generating a response, an error page containing the stack trace is returned instead.

## Dispatching Events

When using the API, the `dispatchFetch` function can be used to dispatch `fetch`events to your Worker. This can be used for testing responses. `dispatchFetch`has the same API as the regular `fetch` method: it either takes a `Request`object, or a URL and optional `RequestInit` object:

JavaScript

```
import { Miniflare, Request } from "miniflare";
const mf = new Miniflare({  modules: true,  script: `  export default {    async fetch(request, env, ctx) {      const body = JSON.stringify({        url: event.request.url,        header: event.request.headers.get("X-Message"),      });      return new Response(body, {        headers: { "Content-Type": "application/json" },      });    })  }  `,});
let res = await mf.dispatchFetch("http://localhost:8787/");console.log(await res.json()); // { url: "http://localhost:8787/", header: null }
res = await mf.dispatchFetch("http://localhost:8787/1", {  headers: { "X-Message": "1" },});console.log(await res.json()); // { url: "http://localhost:8787/1", header: "1" }
res = await mf.dispatchFetch(  new Request("http://localhost:8787/2", {    headers: { "X-Message": "2" },  }),);console.log(await res.json()); // { url: "http://localhost:8787/2", header: "2" }
```

When dispatching events, you are responsible for adding [CF-\* headers](https://developers.cloudflare.com/fundamentals/reference/http-headers/) and the [cf object](https://developers.cloudflare.com/workers/runtime-apis/request#incomingrequestcfproperties). This lets you control their values for testing:

JavaScript

```
const res = await mf.dispatchFetch("http://localhost:8787", {  headers: {    "CF-IPCountry": "GB",  },  cf: {    country: "GB",  },});
```

## Upstream

Miniflare will call each `fetch` listener until a response is returned. If no response is returned, or an exception is thrown and `passThroughOnException()`has been called, the response will be fetched from the specified upstream instead:

JavaScript

```
import { Miniflare } from "miniflare";
const mf = new Miniflare({  script: `  addEventListener("fetch", (event) => {    event.passThroughOnException();    throw new Error();  });  `,  upstream: "https://miniflare.dev",});// If you don't use the same upstream URL when dispatching, Miniflare will// rewrite it to match the upstreamconst res = await mf.dispatchFetch("https://miniflare.dev/core/fetch");console.log(await res.text()); // Source code of this page
```

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