diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9e0f0f807d5..bc4f2e17b15 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -1,14 +1,5 @@
 version: 2
 
-unit_tests: &unit_tests
-  steps:
-    - checkout
-    - restore_cache:
-        key: dependency-cache-{{ checksum "package-lock.json" }}
-    - run:
-        name: Run unit tests.
-        command: npm run ci:test
-
 jobs:
   analysis:
     docker:
@@ -18,13 +9,13 @@ jobs:
       - restore_cache:
           key: dependency-cache-{{ checksum "package-lock.json" }}
       - run:
-          name: Install Dependencies
+          name: Installing Dependencies
           command: npm ci --ignore-scripts
       - run:
-          name: Run linting.
+          name: Running linting
           command: npm run ci:lint
       - run:
-          name: Run NPM Security Audit
+          name: Running NPM Security Audit
           command: npm run security
       - save_cache:
           key: dependency-cache-{{ checksum "package-lock.json" }}
@@ -33,7 +24,20 @@ jobs:
   node-v10-latest:
     docker:
       - image: rollupcabal/circleci-node-v10:latest
-    <<: *unit_tests
+    steps:
+      - checkout
+      - restore_cache:
+          key: dependency-cache-{{ checksum "package-lock.json" }}
+      - run:
+          name: Running tests
+          command: npm run ci:test
+      - store_artifacts:
+          name: Storing browser build for REPL
+          path: /home/circleci/project/dist/rollup.browser.js
+          destination: rollup.browser.js
+      - run:
+          name: Post REPL comment
+          command: ./scripts/post-comment.js
   node-v12-latest:
     docker:
       - image: rollupcabal/circleci-node-v12:latest
@@ -42,9 +46,10 @@ jobs:
       - restore_cache:
           key: dependency-cache-{{ checksum "package-lock.json" }}
       - run:
-          name: Run tests with coverage.
+          name: Running tests with coverage
           command: npm run ci:coverage
 
+
 workflows:
   version: 2
   validate-test:
diff --git a/.eslintrc.json b/.eslintrc.json
index e35395ba7e3..5925f36e338 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -32,7 +32,7 @@
         "plugin:import/warnings"
     ],
     "parserOptions": {
-        "ecmaVersion": 6,
+        "ecmaVersion": 2018,
         "sourceType": "module"
     },
     "settings": {
diff --git a/package.json b/package.json
index 1c2105a002c..09b8917dc3e 100644
--- a/package.json
+++ b/package.json
@@ -97,6 +97,7 @@
     "micromatch": "^4.0.2",
     "minimist": "^1.2.0",
     "mocha": "^6.2.2",
+    "node-fetch": "^2.6.0",
     "nyc": "^15.0.0",
     "prettier": "^1.19.1",
     "pretty-bytes": "^5.3.0",
diff --git a/scripts/post-comment.js b/scripts/post-comment.js
new file mode 100755
index 00000000000..1532fa65085
--- /dev/null
+++ b/scripts/post-comment.js
@@ -0,0 +1,60 @@
+#!/usr/bin/env node
+
+const path = require('path');
+const fetch = require('node-fetch');
+
+const authToken = process.env.GH_AUTH_TOKEN;
+if (!authToken) {
+	throw new Error('Could not find auth token.');
+}
+
+const prNumber = path.basename(
+	process.env.CIRCLE_PULL_REQUEST || process.env.CI_PULL_REQUEST || ''
+);
+if (!prNumber) {
+	console.log('No pull request number found');
+	process.exit(0);
+}
+
+const headline = '### Thank you for your contribution! ❤️';
+
+postComment();
+
+async function postComment() {
+	const existingId = await findExistingComment();
+	console.log(existingId ? `Update comment ${existingId}` : 'Create new comment.');
+	const installPath = await getInstallPath();
+	const path = existingId ? `issues/comments/${existingId}` : `issues/${prNumber}/comments`;
+	const method = existingId ? 'PATCH' : 'POST';
+	await fetch(getApiUrl(path), {
+		method,
+		body: JSON.stringify({
+			body: `${headline}
+
+You can try out this pull request locally via
+
+\`\`\`
+npm install ${installPath}
+\`\`\`
+
+or load it into the REPL:
+https://rollupjs.org/repl/?circleci=${process.env.CIRCLE_BUILD_NUM}
+`
+		})
+	});
+}
+
+async function findExistingComment() {
+	const comments = await (await fetch(getApiUrl(`issues/${prNumber}/comments`), {})).json();
+	const existingComment = comments.find(comment => comment.body.startsWith(headline));
+	return existingComment && existingComment.id;
+}
+
+async function getInstallPath() {
+	const prInfo = await (await fetch(getApiUrl(`pulls/${prNumber}`), {})).json();
+	return `${prInfo.head.repo.full_name}#${prInfo.head.ref}`;
+}
+
+function getApiUrl(path) {
+	return `https://${authToken}:x-oauth-basic@api.github.com/repos/rollup/rollup/${path}`;
+}