TypeScript · Junior · Question 56 of 75

What does `if (count)` miss when `count: number | undefined`?

✓Correct answer: It also excludes 0, which may be a valid value
2Nothing - it only excludes undefined
3It excludes negative numbers

Explanation

Truthiness narrowing treats 0, '' and NaN as false. Use count !== undefined when zero is meaningful.

Further reading

TS Handbook: Narrowing ↗

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