Mimicking Lookbehind in JavaScript

Unlike lookaheads, JavaScript doesn't support regex lookbehind syntax. That's unfortunate, but I'm not content with just resigning to that fact. Following are three ways I've come up with to mimic lookbehinds in JavaScript. For those not familar with the concept of lookbehinds, they are zero-width assertions which, like the more specific \b, ^, and $ metacharacters, don't actually consume anything