pitfall when return string in via json in rails

Today we met a weird problem when return a string via json.

Here is the coffee script code:

Front End

$.post serverUrl, data, (status) ->
	console.log status

And here is our controller:

Backend Action

def action
	# do some complex logic

	render json: "success"
end

Code looks perfect, but we found that the callback is never called! When we check the network traffic, you will found that server does send its response “success”, but the callback is not called!

After spending half an hour to struggle against the jQuery, we finally find the problem!

The reason is that success is not a valid json data! A valid json string should be quoted with “”, or JSON parser will treat it as token, like true or false or nil.

So to fix the problem, we need to change our action code:

Fixed Backend Action

def action
	# do some complex logic

	render json: '"success"'
end

This is really a pitfall, since the wrong code looks so nature!