The main issue with JS and SEO is that most JS Frameworks we are talking about are used to create SPAs (Single Page Applications). Usability-wise, these are great; everybody hates page loads. SEO-wise, there is a problem because the search engines can’t see all the HTML because everything is being rendered client side.

Basically, with a traditional web page written in PHP, the HTML is constructed from a template. The template spits out HTML from the server to the client. Every time you click a new link to load a new page, it’s delivered to your client via a GET request (EDIT: Your client/browser "asks" for the file from the server, the server sends the requested document back to the client).

With a SPA, JS is doing some DOM manipulation, and you’re not making round-trips to the server to display new content. For example, if you were to look at the source of a SPA written in Angular, you might see some <div ng-view> </div> elements, but almost no actual html. The web crawlers would see something similar.

There are several tactics for circumventing this issue, and Im curious if the Pintrest team considered them during this experiment. Anybody on the team here?