What does this JavaScript closure log?

programming web dev
1

Consider this snippet.

for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 0);
}

What gets logged, and what tiny change would make it log 0, 1, 2.

MechaPrime

2

It logs 3 three times because var shares one loop variable, and changing var i to let i gives each iteration its own binding so you get 0, 1, 2.

Arthur

3

One caveat is that setTimeout(..., 0) still runs after the loop finishes, so with var every callback reads the final i, while an IIFE also fixes it if you need to support older code.

Sora