[shermantanktop]

Oh! I didn’t have a name for this one, but it’s a lesson I’ve learned. E.g. if variable x is non-zero, then variable y will be set to zero. Don’t check variable y to find out whether x is zero. And definitely don’t repurpose y for some other function in cases where it’s otherwise unused.

[pc86]

For modern day web developers there are very, very, very few things that fall into the "if you do this you should probably be escorted out of the building on the first offense" category, but "reusing a variable because it's 'not being used'" might be on that list. I can maybe see the argument in very low memory embedded systems or similar systems where I'm not even qualified to come up with examples but not in anything that regularly shows up on HN for example.