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JavaScript Brain Teasers: Exercise Your Mind

Discussion: The Permanent Closure

Understand how JavaScript closures work with loop variables by analyzing a common puzzle involving var and unexpected output. Learn to resolve this using let and IIFE techniques, improving your ability to write predictable, encapsulated functions.

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Verifying the output

Now, it’s time to execute the code and observe the output.

Javascript (babel-node-es2024)
function createCounterArray() {
    const counterArray = [];
    for (var i = 0; i < 5; i++) {
        counterArray.push(() => {
            console.log(`Counter: ${i}`);
        });
    }
    return counterArray;
}
const counters = createCounterArray();
counters.forEach(counter => counter());

Understanding the output

In this puzzle, the intention is to create an array of closure functions, each printing the ...