Why does a var loop print 3 three times?

Definition:

The var loop creates one shared function-scoped binding for i. Every callback closes over that same binding, and the loop has already set it to 3 before the timer callbacks run. Using let in the loop header creates a separate binding for each iteration.

Example and explanation:

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

• All callbacks share the same i; its value is 3 when they run.

• Use let to create a separate binding per iteration: output becomes 0 1 2.

• This is a closure-and-scope issue, not a timer choosing random values.

• You can also capture each value through a separate function parameter, but let is clearer for this case.

Interview point:

• Closures remember bindings, which is why all callbacks can observe the final value of one shared variable.