What gets logged?

for (var i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 1000)
}

A little throw back for all you old heads. This used to be everyone’s favorite JavaScript interview question.

This code will log 5 5 times.

The reason for this is because we declared our variable with var, which is function scoped. By the time our functions given to setTimeout run, i will already be 5 and every function will reference that same variable. To fix this, use let which is block scoped and will give each iteration of our for loop its own i.

for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 1000)
}