diff --git a/.github/workflows/branch.yml b/.github/workflows/branch.yml
index 67b2d0ae..d1ff7881 100644
--- a/.github/workflows/branch.yml
+++ b/.github/workflows/branch.yml
@@ -10,10 +10,10 @@ jobs:
     name: Install
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Cache node_modules
       id: cacheModules
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -25,12 +25,14 @@ jobs:
     name: Debug
     runs-on: ubuntu-latest
     steps:
-    - uses: hmarr/debug-action@v2
+    - uses: hmarr/debug-action@v3
 
   checks:
     name: Check
     needs: [install]
     uses: ./.github/workflows/checks.yml
+    with:
+      ref: ${{ github.sha }}
 
   # The security job can't run on pull requests opened from forks because
   # Github doesn't pass down the SNYK_TOKEN environment variable.
@@ -39,8 +41,8 @@ jobs:
     needs: [install]
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
diff --git a/.github/workflows/checks.yml b/.github/workflows/checks.yml
index 6dc5a19f..932d476a 100644
--- a/.github/workflows/checks.yml
+++ b/.github/workflows/checks.yml
@@ -1,6 +1,13 @@
 name: v4.x checks
 
-on: [workflow_call]
+on:
+  workflow_call:
+    inputs:
+      ref:
+        description: 'The commit the workflow should check out'
+        required: true
+        default: ${{ github.sha }}
+        type: string
 
 jobs:
   test-node:
@@ -12,13 +19,15 @@ jobs:
         node-version: [14.x, 16.x, 18.x, 20.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ inputs.ref }}
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
     - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v3
+      uses: actions/setup-node@v4
       with:
         node-version: ${{ matrix.node-version }}
     - run: npm install --prefer-offline
@@ -28,13 +37,15 @@ jobs:
     name: Browser Test Specs
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ inputs.ref }}
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
     - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v3
+      uses: actions/setup-node@v4
       with:
         node-version: ${{ matrix.node-version }}
     - run: npm install --prefer-offline
@@ -44,8 +55,10 @@ jobs:
     name: Code Lint
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ inputs.ref }}
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -56,8 +69,10 @@ jobs:
     name: Types
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ inputs.ref }}
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 464d1729..d0a72612 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -22,16 +22,18 @@ jobs:
     name: Debug
     runs-on: ubuntu-latest
     steps:
-    - uses: hmarr/debug-action@v2
+    - uses: hmarr/debug-action@v3
 
   install:
     name: Install
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
     - name: Cache node_modules
       id: cacheModules
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -43,3 +45,5 @@ jobs:
     name: Checks
     needs: [install]
     uses: ./.github/workflows/checks.yml
+    with:
+      ref: ${{ github.event.pull_request.head.sha }}
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index c064dba8..5333a3a6 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -16,10 +16,10 @@ jobs:
     name: Install
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Cache node_modules
       id: cacheModules
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.npm # cache where "npm install" uses before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -31,7 +31,7 @@ jobs:
     name: Debug
     runs-on: ubuntu-latest
     steps:
-    - uses: hmarr/debug-action@v2
+    - uses: hmarr/debug-action@v3
 
   checks:
     name: Check
@@ -45,8 +45,8 @@ jobs:
     needs: [install]
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/cache@v3
+    - uses: actions/checkout@v4
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # cache where "npm install" uses before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
@@ -60,13 +60,13 @@ jobs:
     runs-on: ubuntu-latest
     needs: [checks, security]
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/setup-node@v3
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
       with:
         node-version-file: '.nvmrc'
         # Setup .npmrc file to publish to npm
         registry-url: 'https://registry.npmjs.org'
-    - uses: actions/cache@v3
+    - uses: actions/cache@v4
       with:
         path: ~/.npm # this is cache where npm installs from before going out to the network
         key: ${{ runner.os }}-node-${{ hashFiles('**/package.json') }}
diff --git a/.nvmrc b/.nvmrc
index 8351c193..209e3ef4 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-14
+20
diff --git a/Makefile b/Makefile
index c0ca39e5..425e9230 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,5 @@
+include makefiles/*.mk
+
 .PHONY: all
 all: test lint typecheck
 
@@ -40,120 +42,3 @@ test/fetch-api/api.spec.js: test/fetch-api/api.spec.ts
 	@echo ""
 	@echo "=> make $@"
 	@npx tsc
-
-
-##
-# Checks
-
-.PHONY: commitlint
-commitlint: node_modules
-	npx commitlint --from origin/main --to HEAD --verbose
-
-.PHONY: cov
-cov:
-	npx nyc report --reporter=text-lcov > .reports/coverage.lcov && npx codecov
-
-.PHONY: lint
-lint:
-	@echo ""
-	@echo "=> make $@"
-	@npx standard
-
-.PHONY: secure
-secure:
-	@echo ""
-	@echo "=> make $@"
-	@npx snyk test
-
-.PHONY: typecheck
-typecheck:
-	@echo ""
-	@echo "=> make $@"
-	@npx tsc --lib ES6 --noEmit index.d.ts ./test/fetch-api/api.spec.ts
-
-
-##
-# Test groups
-
-.PHONY: test
-test: | test-browser test-node
-
-.PHONY: test-browser
-test-browser: |\
-	test-fetch-browser-native \
-	test-fetch-browser-whatwg \
-  test-fetch-browser-service-worker \
-	test-module-web-cjs \
-	test-module-web-esm \
-	test-module-react-native
-
-.PHONY: test-node
-test-node: |\
-	test-fetch-node-native \
-	test-fetch-node-fetch \
-	test-module-node-cjs \
-	test-module-node-esm
-
-
-##
-# Test units
-
-.PHONY: test-fetch-browser-native
-test-fetch-browser-native: | dist test/fetch-api/api.spec.js
-	@echo ""
-	@echo "=> make $@"
-	@./test/fetch-api/browser/run.sh
-
-.PHONY: test-fetch-browser-whatwg
-test-fetch-browser-whatwg: | dist test/fetch-api/api.spec.js
-	@echo ""
-	@echo "=> make $@"
-	@./test/fetch-api/whatwg/run.sh
-
-.PHONY: test-fetch-browser-service-worker
-test-fetch-browser-service-worker: dist test/fetch-api/api.spec.js
-	@echo ""
-	@echo "=> make $@"
-	@./test/fetch-api/service-worker/run.sh
-
-.PHONY: test-fetch-node-native
-test-fetch-node-native: | dist test/fetch-api/api.spec.js
-	@echo ""
-	@echo "=> make $@"
-	@./test/fetch-api/node/run.sh
-
-.PHONY: test-fetch-node-fetch
-test-fetch-node-fetch: | dist test/fetch-api/api.spec.js
-	@echo ""
-	@echo "=> make $@"
-	@./test/fetch-api/node-fetch/run.sh
-
-.PHONY: test-module-web-cjs
-test-module-web-cjs: | dist
-	@echo ""
-	@echo "=> make $@"
-	@./test/module-system/web.cjs/run.sh
-
-.PHONY: test-module-web-esm
-test-module-web-esm: | dist
-	@echo ""
-	@echo "=> make $@"
-	@./test/module-system/web.esm/run.sh
-
-.PHONY: test-module-node-cjs
-test-module-node-cjs: | dist
-	@echo ""
-	@echo "=> make $@"
-	@./test/module-system/node.cjs/run.sh
-
-.PHONY: test-module-node-esm
-test-module-node-esm: | dist
-	@echo ""
-	@echo "=> make $@"
-	@./test/module-system/node.esm/run.sh
-
-.PHONY: test-module-react-native
-test-module-react-native: | dist
-	@echo ""
-	@echo "=> make $@"
-	@./test/module-system/react-native/run.sh
diff --git a/bin/is-port-in-use b/bin/is-port-in-use
new file mode 100755
index 00000000..5efbd743
--- /dev/null
+++ b/bin/is-port-in-use
@@ -0,0 +1,17 @@
+#!/usr/bin/env node
+
+const net = require('net')
+const args = process.argv.slice(2)
+const port = args[0] || 8000
+const server = net.createServer().listen(port)
+
+server.on('listening', () => {
+  server.close()
+  console.log('Port ' + port + ' is available.')
+  process.exit(0)
+})
+
+server.on('error', () => {
+  console.log('Port ' + port + ' is in use.')
+  process.exit(1)
+})
diff --git a/makefiles/checks.mk b/makefiles/checks.mk
new file mode 100644
index 00000000..312b9dcc
--- /dev/null
+++ b/makefiles/checks.mk
@@ -0,0 +1,30 @@
+
+##
+# Checks
+
+.PHONY: commitlint
+commitlint: node_modules
+	npx commitlint --from origin/main --to HEAD --verbose
+
+.PHONY: cov
+cov:
+	npx nyc report --reporter=text-lcov > .reports/coverage.lcov && npx codecov
+
+.PHONY: lint
+lint:
+	@echo ""
+	@echo "=> make $@"
+	@npx standard
+
+.PHONY: secure
+secure:
+	@echo ""
+	@echo "=> make $@"
+	@npx snyk test
+
+.PHONY: typecheck
+typecheck:
+	@echo ""
+	@echo "=> make $@"
+	@npx tsc --lib ES6 --noEmit index.d.ts ./test/fetch-api/api.spec.ts
+
diff --git a/makefiles/test.mk b/makefiles/test.mk
new file mode 100644
index 00000000..736ffc79
--- /dev/null
+++ b/makefiles/test.mk
@@ -0,0 +1,86 @@
+
+##
+# Test groups
+
+.PHONY: test
+test: | test-browser test-node
+
+.PHONY: test-browser
+test-browser: |\
+	test-fetch-browser-native \
+	test-fetch-browser-whatwg \
+  test-fetch-browser-service-worker \
+	test-module-web-cjs \
+	test-module-web-esm \
+	test-module-react-native
+
+.PHONY: test-node
+test-node: |\
+	test-fetch-node-native \
+	test-fetch-node-fetch \
+	test-module-node-cjs \
+	test-module-node-esm
+
+
+##
+# Test units
+
+.PHONY: test-fetch-browser-native
+test-fetch-browser-native: | dist test/fetch-api/api.spec.js
+	@echo ""
+	@echo "=> make $@"
+	@./test/fetch-api/browser/run.sh
+
+.PHONY: test-fetch-browser-whatwg
+test-fetch-browser-whatwg: | dist test/fetch-api/api.spec.js
+	@echo ""
+	@echo "=> make $@"
+	@./test/fetch-api/whatwg/run.sh
+
+.PHONY: test-fetch-browser-service-worker
+test-fetch-browser-service-worker: dist test/fetch-api/api.spec.js
+	@echo ""
+	@echo "=> make $@"
+	@./test/fetch-api/service-worker/run.sh
+
+.PHONY: test-fetch-node-native
+test-fetch-node-native: | dist test/fetch-api/api.spec.js
+	@echo ""
+	@echo "=> make $@"
+	@./test/fetch-api/node/run.sh
+
+.PHONY: test-fetch-node-fetch
+test-fetch-node-fetch: | dist test/fetch-api/api.spec.js
+	@echo ""
+	@echo "=> make $@"
+	@./test/fetch-api/node-fetch/run.sh
+
+.PHONY: test-module-web-cjs
+test-module-web-cjs: | dist
+	@echo ""
+	@echo "=> make $@"
+	@./test/module-system/web.cjs/run.sh
+
+.PHONY: test-module-web-esm
+test-module-web-esm: | dist
+	@echo ""
+	@echo "=> make $@"
+	@./test/module-system/web.esm/run.sh
+
+.PHONY: test-module-node-cjs
+test-module-node-cjs: | dist
+	@echo ""
+	@echo "=> make $@"
+	@./test/module-system/node.cjs/run.sh
+
+.PHONY: test-module-node-esm
+test-module-node-esm: | dist
+	@echo ""
+	@echo "=> make $@"
+	@./test/module-system/node.esm/run.sh
+
+.PHONY: test-module-react-native
+test-module-react-native: | dist
+	@echo ""
+	@echo "=> make $@"
+	@./test/module-system/react-native/run.sh
diff --git a/package.json b/package.json
index 30f06907..c88009b7 100644
--- a/package.json
+++ b/package.json
@@ -73,7 +73,6 @@
   "devDependencies": {
     "@commitlint/cli": "17.6.6",
     "@commitlint/config-conventional": "17.6.6",
-    "@rollup/plugin-terser": "0.4.3",
     "@types/chai": "4.3.5",
     "@types/mocha": "10.0.1",
     "@types/node": "18.15.13",
@@ -92,6 +91,8 @@
     "rimraf": "5.0.1",
     "rollup": "3.26.0",
     "rollup-plugin-copy": "3.4.0",
+    "rollup-plugin-esbuild": "6.1.1",
+    "rollup-plugin-esbuild-minify": "1.1.2",
     "semver": "7.5.3",
     "serve-index": "1.9.1",
     "standard": "17.1.0",
diff --git a/rollup.config.js b/rollup.config.js
index dfd00e5d..0958bd28 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -1,7 +1,7 @@
 /* Rollup creates the browser version of the polyfill and ponyfill. */
 import path from 'path'
 import copy from 'rollup-plugin-copy'
-import terser from '@rollup/plugin-terser'
+import { minify } from 'rollup-plugin-esbuild'
 
 const input = path.join(__dirname, 'node_modules', 'whatwg-fetch', 'fetch.js')
 
@@ -128,7 +128,7 @@ export default [
       `)
     },
     plugins: [
-      terser()
+      minify()
     ]
   }
 ]
diff --git a/test/setup/server.sh b/test/setup/server.sh
index f9ecb62d..337cc5cb 100644
--- a/test/setup/server.sh
+++ b/test/setup/server.sh
@@ -11,7 +11,7 @@ kill_server() {
 }
 
 is_server_ready() {
-  lsof -i :8000 > /dev/null
+  ./bin/is-port-in-use > /dev/null
 }
 
 wait_server() {