CERN


for (var i = 0; i < 5; i++) {}

vs


var i;
for (i = 0; i < 5; i++) {}

Not just Javascript, any language.

First one because the variable will go out of scope after the loop.

Second one because it's compliant C89 code (under the assumption that var is a define or a typedef to the correct type).

>>2
unless it's javascript, of course

>>2


{
    int i;
    for (i = 0; i < 5; i++) {}
}

Now it is C89 compliant and the variable goes out of scope

The first is tighter from a program verification point of view as i's existence affects a lesser region of code. With the second one you at least know for sure there won't be any wasted instructions incrementing and decrementing the stack pointer while entering and exiting scope. I can't be sure what happens on the first (not just language, but compiler dependent) and too lazy to check, it could be equivalent emitted instructions after the compiler checks that i isn't used outside for.