I'm going to repost this here because it actually tells me why I'd want to route all my JS through a third party, and I had to click through the blog link below to find it:<p><a href="http://blog.proxino.com/post/8388203148/catching-the-worlds-bugs-instrumentation-via-proxy" rel="nofollow">http://blog.proxino.com/post/8388203148/catching-the-worlds-...</a><p>"At Proxino, there’s one question I receive with uncommon frequency: why the proxy? After all, we only ever (at the moment) handle exceptions for you, and so there is curiosity. Is it really necessary, my customer will ask. He considers, perhaps, that the proxy is some clever ploy, a small glimpse at our plans for world domination. A lovely thought, if only it were so. Developers in particular have a tendency to believe that what Proxino does can be done dynamically. They are mistaken.<p>In a general sense, what Proxino does is a form of global exception handling, a way to catch every exception that occurs within your Javascript. To their credit, our customers correctly suspect that some approximation of this can be achieved dynamically. For it certainly can. Here is a naive first pass attempt at such a global handler, no proxy required:<p>window.onerror = function(e){ console.log(e) }<p>Unfortunately, window.onerror does not work in every browser, nor on every piece of code. It will fail to catch some exceptions raised by elements of jQuery, and other similarly complex libraries. It’s a simple one-liner, and it sort of works. But quite often, sort of is not enough.<p>With a bit more care — and a lot more code — a clever programmer can find dynamic work arounds for most browsers and most popular libraries. However in the general case, a global exception handler constructed dynamically is something of an elusive, asymptotic state. You are simply not going to get there. And this brings me to my point. Proxino is not interested in most. We want to catch, and tell you about, everything that goes wrong in your Javascript. Enter the proxy.<p>When a request reaches proxy.proxino.com, we lookup your existing code, parse it into AST form, and walk down the tree inserting special try/catch blocks within each function definition, as well as around the file itself. We then serve this instrumented file to your users, and handle every exception that occurs. Naturally, we have optimized this process for speed (with caching, etc.) but this guarantees us — and more importantly, you — complete code coverage. You will know about every exception.<p>Dynamic approaches are incredibly convenient in some ways, but in the general case they simply don’t work. And so there is a Good reason for the proxy. Hope this helps."