JavaScript Block Scope: How let, const, and var Differ in Variable Access

Block scope in JavaScript means a variable declared inside a block — defined by curly braces — can only be accessed within that block. The keywords let and const follow block scoping rules, throwing a ReferenceError if accessed outside their declared block. In contrast, var is function-scoped, allowing it to be accessed even outside the block where it was defined. This distinction matters because block scoping helps prevent variables from being unintentionally modified or accessed in unrelated parts of the code. Modern JavaScript development generally favors let and const over var for cleaner, more predictable code.