feat: swap node-fetch for undici (#4)

node-fetch does not use browser streams which makes using it in typed environments very hard since the methods on node streams are different from those on browser streams.

undici is a node implementation of fetch that supports browser streams and is probably the closest thing we'll ever see to fetch in node core, so swap node-fetch for undici.

BREAKING CHANGE: only browser streams are returned, requires node 16+

.aegir.js

@@ -0,0 +1,27 @@
+/** @type {import('aegir').Options["build"]["config"]} */
+const esbuild = {
+  plugins: [
+    {
+      name: 'node built ins',
+      setup (build) {
+        build.onResolve({ filter: /^undici$/ }, () => {
+          return { path: require.resolve('./scripts/undici') }
+        })
+      }
+    }
+  ]
+}
+
+/** @type {import('aegir').PartialOptions} */
+module.exports = {
+  build: {
+    config: esbuild
+  },
+  test: {
+    browser: {
+      config: {
+        buildConfig: esbuild
+      }
+    }
+  }
+}

README.md

@@ -1,27 +1,35 @@
 # native-fetch
 
-> Returns native fetch/Request/Headers if available or the node-fetch module if not
+> Returns native fetch/Request/Headers if available or the `undici` module if not
 
-An (almost) drop-in replacement for the `node-fetch` module that returns the native fetch if available or the polyfill if not.
+An (almost) drop-in replacement for the `undici` module that returns the native fetch if available or the polyfill if not.
 
 ### Why?
 
 Some environments such as the Electron Renderer process straddle the node/browser divide with features from both APIs available.  In these cases the webpack approach of always using the `browser` field in your `package.json` to override requires is too heavy-handed as sometimes you want to use the node version of an API.
 
 Instead we can check for the availability of a given API and return it, rather than the node-polyfill for that API.
 
+### Why Undici and not node-fetch?
+
+[node-fetch](https://www.npmjs.com/package/node-fetch) is the OG fetch implementation for node, but it uses [Node.js streams](https://nodejs.org/api/stream.html) instead of [WHATWG streams](https://streams.spec.whatwg.org/). This means the APIs are not the same which leads to all sorts of weird shenanigans with types.
+
+[undici](https://www.npmjs.com/package/undici) is the new kid on the block and uses WHATWG streams so all of the APIs now live in glorious harmony.
+
+If you are trying to write polymorphic code with strong typing this is a big deal.
+
 ## Install
 
-You must install a version of `node-fetch` [alongside this module](https://docs.npmjs.com/files/package.json#peerdependencies) to be used if a native implementation is not available.
+You must install a version of `undici` [alongside this module](https://docs.npmjs.com/files/package.json#peerdependencies) to be used if a native implementation is not available.
 
 ```console
-$ npm install --save native-fetch node-fetch
+$ npm install --save native-fetch undici
 ```
 
 ## Usage
 
 ```javascript
-const { default: fetch } = require('native-fetch')
+const { fetch } = require('native-fetch')
 
 fetch('https://github.com/')
     .then(res => res.text())

package.json

@@ -1,7 +1,7 @@
 {
   "name": "native-fetch",
   "version": "3.0.0",
-  "description": "Returns native fetch if available or the node-fetch module if not",
+  "description": "Returns native fetch if available or the undici module if not",
   "main": "src/index.js",
   "types": "dist/src/index.d.ts",
   "files": [
@@ -11,7 +11,7 @@
   "scripts": {
     "test": "aegir test -t node -t browser -t webworker -t electron-main -t electron-renderer",
     "lint": "aegir lint && aegir ts -p check",
-    "prepare": "aegir build --no-bundle",
+    "build": "aegir build --no-bundle",
     "release": "aegir release --docs false",
     "release-minor": "aegir release --type minor --docs false",
     "release-major": "aegir release --type major --docs false"
@@ -23,12 +23,11 @@
     "url": "git+https://github.com/achingbrain/native-fetch.git"
   },
   "peerDependencies": {
-    "node-fetch": "*"
+    "undici": "*"
   },
   "devDependencies": {
-    "@types/node-fetch": "^2.5.8",
-    "aegir": "^30.3.0",
-    "node-fetch": "^2.6.0"
+    "aegir": "^36.0.0",
+    "undici": "^4.10.0"
   },
   "contributors": [
     "achingbrain <alex@achingbrain.net>"

scripts/undici.js

@@ -0,0 +1,2 @@
+
+module.exports = {}

src/index.js

@@ -1,17 +1,18 @@
 'use strict'
 
+// @ts-expect-error globalThis.fetch is defined according to the env types but it's not in node
 if (globalThis.fetch && globalThis.Headers && globalThis.Request && globalThis.Response) {
   module.exports = {
-    default: globalThis.fetch,
+    fetch: globalThis.fetch,
     Headers: globalThis.Headers,
     Request: globalThis.Request,
     Response: globalThis.Response
   }
 } else {
   module.exports = {
-    default: require('node-fetch').default,
-    Headers: require('node-fetch').Headers,
-    Request: require('node-fetch').Request,
-    Response: require('node-fetch').Response
+    fetch: require('undici').fetch,
+    Headers: require('undici').Headers,
+    Request: require('undici').Request,
+    Response: require('undici').Response
   }
 }

test/index.spec.js

@@ -3,35 +3,35 @@
 /* eslint-env mocha */
 const { expect } = require('aegir/utils/chai')
 const NativeFetch = require('../src')
-const NodeFetch = require('node-fetch')
+const Undici = require('undici')
 
 describe('env', function () {
   it('fetch should be correct in each env', function () {
     switch (process.env.AEGIR_RUNNER) {
       case 'electron-main':
-        expect(NativeFetch.default).to.equal(NodeFetch.default)
+        expect(NativeFetch.fetch).to.equal(Undici.fetch)
         expect(globalThis.fetch).to.be.undefined()
         break
       case 'electron-renderer':
-        expect(NativeFetch.default).to.equal(globalThis.fetch)
+        expect(NativeFetch.fetch).to.equal(globalThis.fetch)
         expect(NativeFetch.Headers).to.equal(globalThis.Headers)
         expect(NativeFetch.Request).to.equal(globalThis.Request)
         expect(NativeFetch.Response).to.equal(globalThis.Response)
         expect(globalThis.fetch).to.be.ok()
         break
       case 'node':
-        expect(NativeFetch.default).to.equal(NodeFetch.default)
+        expect(NativeFetch.fetch).to.equal(Undici.fetch)
         expect(globalThis.fetch).to.be.undefined()
         break
       case 'browser':
-        expect(NativeFetch.default).to.equal(globalThis.fetch)
+        expect(NativeFetch.fetch).to.equal(globalThis.fetch)
         expect(NativeFetch.Headers).to.equal(globalThis.Headers)
         expect(NativeFetch.Request).to.equal(globalThis.Request)
         expect(NativeFetch.Response).to.equal(globalThis.Response)
         expect(globalThis.fetch).to.be.ok()
         break
       case 'webworker':
-        expect(NativeFetch.default).to.equal(globalThis.fetch)
+        expect(NativeFetch.fetch).to.equal(globalThis.fetch)
         expect(NativeFetch.Headers).to.equal(globalThis.Headers)
         expect(NativeFetch.Request).to.equal(globalThis.Request)
         expect(NativeFetch.Response).to.equal(globalThis.Response)