Why does my closure not retain the value of a loop variable in a setTimeout callback?

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Why does my closure not retain the value of a loop variable in a setTimeout callback?

Asked on Jan 09, 2026

Answer

Closures in JavaScript capture variables by reference, not by value. In a loop, this can lead to unexpected behavior when using functions like "setTimeout". Here's how you can correctly capture the loop variable using "let" or an IIFE.

<!-- BEGIN COPY / PASTE -->
        for (let i = 0; i < 3; i++) {
            setTimeout(() => {
                console.log(i);
            }, 1000);
        }
        <!-- END COPY / PASTE -->

Additional Comment:

Using "let" in the loop declaration creates a new block scope for each iteration, capturing the current value of "i".
Alternatively, you can use an Immediately Invoked Function Expression (IIFE) to create a new scope for each iteration if "var" is used.
This ensures that each "setTimeout" callback retains the correct value of "i" when it executes.

✅ Answered with JavaScript best practices.

Ask any question about JavaScript here... and get an instant response.

Why does my closure not retain the value of a loop variable in a setTimeout callback?

Asked on Jan 09, 2026

Answer

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