Should you use const or let for loop variables in JavaScript?
Use let for classic for loop counters (they increment). Use const for for...of and for...in (each iteration is a fresh binding that does not change within the iteration). Never use var for loop variables in modern code.
Verify This Answer
Cross-check this information using these trusted sources:
More FAQs in Best Practices for Block Scope in JavaScript
Use const by default and let for reassignable variables. Keep variables in the tightest scope possible. Use let in classic for loops, const in for...of and for...in. Wrap switch cases in braces. Avoid shadowing. Do not close over large objects unnecessarily.
Tighter scope means fewer bugs (variables are not visible where they are not needed), better garbage collection (variables are freed sooner), and more readable code (intent is clear).
Wrap each case in braces to give it its own block scope. Without braces, all cases share one scope, and re-declaring let or const with the same name throws SyntaxError.
Still have questions?
Browse all our FAQs or reach out to our support team