One of Cogneato’s clients noticed that Recaptcha wasn’t working on their site. The checkbox wouldn’t check at all. I noticed that there was an error like “Unexpected token in JSON at position 0” in the browser’s console log. Since this was one of our really old sites, I figured it might have some sort of inadequate polyfill for JSON.parse(). I saw that the site was using Prototype.js, so I looked through the script to see if it was overriding that method, but it wasn’t. That did put me on the right track, though, to find the Stackoverflow answer that solved it for me.
Prototype was overriding the now browser standard reduce() method of Array.prototype with its own, incompatible functionality. The solution was simply to remove that method from the “prototype.js” file. We weren’t using the special Prototype functionality anywhere, so this didn’t cause a problem. If we were, we’d probably have to duck punch the browser’s functionality to handle both method signatures.