JavaScript · Middle · Question 69 of 75

Why convert a large list of allowed IDs to a `Set` before many lookups?

✓Correct answer: set.has(x) is about constant time, while array.includes(x) scans the whole array each time
2Sets use less memory than arrays
3Arrays can't contain numbers as IDs

Explanation

For one lookup it doesn't matter; for thousands inside a loop, O(n) per check turns into O(n²) overall.

Further reading

javascript.info: Map and Set ↗

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