The answer
Any code wrapped in a pair of braces {}. Blocks appear in if statements, for and while loops, try...catch, and as standalone blocks. let and const declared inside any of these are block-scoped.
What Is Block Scope in JavaScript?
What counts as a block in JavaScript?
More FAQs in What Is Block Scope in JavaScript?
Variables declared with let and const inside a pair of braces are only accessible inside those braces. var is not block-scoped; it is function-scoped and leaks out of blocks.
Yes. var is function-scoped, not block-scoped. A var inside an if or a standalone block is hoisted to the enclosing function or global scope. let and const do not leak.
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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