Rails : Rendered HTML as JSON value

17 Sep 2014

When SJR(Server-generated JavaScript Responses) was first introduced to me by @sunilkumar_g56, I was not much impressed until I actually use it my project. Yes, they are really handy and helps you to work done really faster. But one thing I hate about is writing a part of JavaScript in the rails views as .js.erb.

I found it bit difficult to read the code using SJR because while I read the ajax action in some JS file and then I need to go into some other file to know what happens when it is success/failure. Also if you are use Constructor pattern for your components, its difficult to access even the public methods in SJR. So I like to return the response of the ajax request and do the DOM manipulation on success and failure in module itself.

If the ajax response is just some HTML and you need to make change only in one location on DOM, you just need to render the partial/view, but when you have multiple data to return as ajax response and need to make DOM changes in multiple areas we need to return the response as JSON.

You might now think that what so difficult to do it? Me too thought the same until I need to return a rendered HTML as the value in JSON. The jQuery.ajax function started throwing error saying parseerror to the returned json.

To fix this you need to run to_json on the rendered HTML,

  "status": "success",
  "html": {
      "products": <%= (render partial: 'show.html').to_json.html_safe %>
  "data": {
    "count": <%= @products["search_count"] %>

So you might be wondering whether the String class have a method named to_json, No, but render method really returns EscapedString which have a to_json method on it. You can see the source in activesupport/lib/active_support/json/encoding.rb

This to_json method will escape <, >, and & to unicode chars.

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