Similarly, copying code from StackOverflow, Github and random blogs have all worked without any issues.

So it can't be as easy as you imply.

Mixed spaces and tabs as a next go, and it worked too---converting the pasted tabs into spaces of my style.

Smart-tabbing is pretty smart.

Granted, I knew that so long as the indents were proper (i.e it compiles), that pasting at that point would give valid code but... I can't see how using braces would have been different. Just because it compiles, doesn't mean it works. I've pasted javascript incorrectly multiple time to produce valid, but incorrect for my needs code.

The indentation strategy also looks to produce syntactically valid code, so long as what you are pasting lacked indentation errors.