unexplainable 500 errors with flask and jquery ajax on google app engine

I was trying to do something simple - get a preloaded partial from the server via ajax. my api call worked directly in the browser, worked when I ran it with $.get() from the console after the page was loaded, but was returning 500 during page load (as in, only failing when it was called as js running at after dom load). I could confirm that the correct flask view was running and succeeding using logging, but the 500 I was getting had NO responsetext, and nothing useful..

After fighting and fruitless searching for 40 minutes, I disabled the flask debug toolbar. Voila! everything worked as expected.

Moral of the story: F$@# the flask debug toolbar.

facepalms: 8

Rails 3 Unobtrusive Javascript is Unintuitve

So what I wanted to do was link from a partial view to a controller method through a route which took a title parameter and from the controller method run a javascript file in order to append content to a div with a unique name defined by the title param.

In django it's pretty straightforward, but ruby on rails 3 had me scratching my head for a good long while.

Here's the solution, or at least the parts that were difficult:

the link:

<%= link_to "Comments", show_comments_path( :format => 'js', :comment_id=> session[:id] ), :remote => true %>

This whole :remote => true business tells rails 3 that this is an ajax call. The :format param does NOT get passed into the url, but DOES render the response as html, most of the time. Which is to say, rails will run the .js.erb file with the name matching your route.

Here's the route:

match 'show_comments/:comment_id', :to => 'deals#show_comments', :as => :show_comments

So first rails runs the show_comments method from the appropriate controller, which you can use to set state variables for the javascript. Then, whatever is in show_comments.js.erb will be run, and the current page will NOT be reloaded or redirected. No partial needed. No view needed. The controlling method will do all of this as the default return, so no return or render needed either, only the .js.erb file which has your prototype or jquery calls, or whathaveyou.

facepalms: 4 (steady, slow, only slightly infuriating progress)