What is block scope in JavaScript?
Variables declared with let and const are only accessible inside the nearest pair of braces. This applies to if blocks, for loops, try/catch, and plain blocks. var is not block-scoped and leaks out.
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More FAQs in Block Scope with let and const: Examples
Yes. Each iteration of for...of creates a fresh binding, and the loop variable does not change within an iteration. Use const for for...of and for...in. Use let only for classic for loops where the counter increments.
No. let is block-scoped, so the loop variable stays inside the loop. var is function-scoped and leaks out, which is one reason to prefer let in loops.
Yes. The err in catch (err) is block-scoped to the catch block. It is not accessible outside the catch, and it does not leak to the outer scope.
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