js-for.md

A

for (init; check; update) {
	...
}

B

init;
while(check) {
	...
	update;
}

A and B are the same.

If thing is an Array

A

for (var i in thing)

B

for (var i = 0; i < thing.length; i++)

A and B are the same.

Normal for-loop usage

for (var i = start; i <= end; i++)