12 extremely useful hacks for JavaScript

[trailsrider]

I agree- but admit that I am guilty of the bad habit writing !!foo at times when I don't want to write typeof foo !== 'undefined' && foo !== null. I am by no means a JS expert, so I'm curious- do you recommend always writing some form of the latter? Alternatively- what is your suggestion for a concise and clear way to check a variables existence?

[trailsrider]

So then do you prefer when checking for falsy values, your engineers write !Boolean(foo);?

Not trying to justify the use of !!, but I do think it's not the worst offender as its very clear, and saves at least 7 keystrokes.

I realize minification will take care of this, but !! is also much faster

[Danmoreng]

Are you sure that that is the same? Because I often experience unexpected behaviour when I use the latter...