You’ve written your Chrome extension in ClojureScript, whether using Khroma or any other alternative. You have a background script, maybe some content script that gets run on pages, maybe some code for a management UI. Everything’s fine on development, but when you’re ready to release and want to apply some optimizations, everything gets bundled together into a single file. Not only you end up with a larger JS that gets loaded multiple times, but your initialization code starts tripping over each other.
I normally do a search, start opening the tabs that seem interesting, and then as I flip through them, I end up opening even more links on tabs as they seem relevant. Next thing I know I have a huge mess of tabs, and it’s hard to remember which one I’ve read or which one is important.
Relevance is a Chrome plugin I wrote to help manage that.
A few weeks ago I wrote a short piece about the available tools for building Chrome extensions in ClojureScript.
Among the tools I reviewed was khroma, a still very much work-in-progress ClojureScript library providing idiomatic access for the Chrome API. One of original comments I had was that khroma was still incomplete, and had some not entirely evident function names.
I have since taken up khroma development and begun extending and refactoring it. However, a question immediately came up: how do we go about testing it? Your first impulse might be to say “why, don’t we have cljs.test?”.
Yes, we do, but we can’t run these tests automatically from the command line: the APIs are only available when you’re running inside Chrome as an extension with the right permissions.
Moreover, I’d like to be able to provide usage samples and data review for the myriad of events you can hook up to, some of which aren’t easily testable because they depend on user input, or asynchronous inter-page communication. How to go about this, then?
Enter devcards.
I recently spent some time pulling my hair at a Chrome extension problem, and it turned out to be something rather silly.
I was attempting to do AJAX requests from an extension to a test local REST service, which I’d written in Clojure using Liberator. GET requests did get to the server, POST didn’t. In either case, however, the extension did not get a reply, and Chrome just reported that it was returning a method not allowed because the resource didn’t have an Access-Control-Allow-Origin header.
This was very odd. First, why would Liberator not fail on GETs at all? Liberator should only return 405 when the request method is not allowed - when did this change, if ever? And then, even if it was a Liberator configuration issue, why would I be able to successfully make requests to it using HTTPie from a terminal?
There’s not as much documentation on building a Chrome extension with ClojureScript, so I thought I’d document my findings on the current state of libraries.
Yes, you can of course build Chrome extensions with ClojureScript, as other articles have pointed out. It’s, after all, just Javascript underneath. There’s some set up involved, and the example given hew closely to the Javascript-way of doing things.
Below are some tools that can help you with a more idiomatic way of doing things in Clojure.