Simplifies code contributions by automating the dev setup with gitpod.io

.gitpod.Dockerfile

@@ -0,0 +1,7 @@
+FROM gitpod/workspace-full-vnc
+
+USER gitpod
+
+RUN sudo apt-get update && \
+    sudo apt-get install -yq firefox && \
+    sudo rm -rf /var/lib/apt/lists/*

.gitpod.yml

@@ -0,0 +1,13 @@
+image:
+  file: .gitpod.Dockerfile
+tasks:
+  - command: |
+      gp await-port 8888 && gp preview $(gp url 8888)/web/viewer.html && echo '[{"name": "Firefox","path": "/usr/bin/firefox"}]' | jq '.' > test/resources/browser_manifests/browser_manifest.json
+
+  - init: npm install -g gulp-cli && npm install
+    command: gulp server
+ports:
+  - port: 8888
+    onOpen: ignore
+  - port: 6080
+    onOpen: ignore

README.md

@@ -71,6 +71,12 @@ It is also possible to view all test PDF files on the right side by opening:
 
 + http://localhost:8888/test/pdfs/?frame
 
+## Online setup with a single click
+
+It's recommended to follow [Getting the Code] above, however you can also use [Gitpod](https://gitpod.io) (a free online VS Code like IDE). With a single click it will launch a ready to use workspace, with all the dependencies pre-installed and the web server running, so that you can start coding straight away.
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/mozilla/pdf.js)
+
 ## Building PDF.js
 
 In order to bundle all `src/` files into two production scripts and build the generic