Preface

In February of 2010, I was on the phone with Jason Yan, CTO and cofounder of a web startup called Disqus. At the time, Disqus was a tiny company behind a fast-growing commenting application, distributed as a third-party script and popular with bloggers and a handful of large media companies. Jason was interviewing me for a JavaScript engineering role—their first hire dedicated to working on a fast-growing client codebase.

After a handful of standard JavaScript interview questions involving classes, prototypes, and scopes, Jason took a different tack. He asked me the following (roughly paraphrased) question: “Let’s say I’ve taken a native function prototype—like Array.prototype.indexOf and assigned it a new value. How would you get the original value back?”

I was dumbstruck. This was a problem I had never encountered before, and I didn’t know the answer. Jason explained to me that the Disqus application executes in environments they don’t control. And in those environments, native properties are sometimes overwritten or mangled, properties that they depend on.

I wasn’t about to give up on the question. So in the middle of the interview, I opened up my browser’s JavaScript console, and started fiddling around with function prototypes. In a few short minutes, I made the startling discovery that you could use JavaScript’s delete operator on a modified native property, and the browser would restore the original value.