Which statement about var, let, and const in JavaScript is true?

Which statement about var, let, and const in JavaScript is true?

• A. Var is block-scoped and cannot be redeclared.
• B. Var is function-scoped and can be redeclared; let and const are block-scoped, with let mutable and const read-only bindings.
• C. Let is function-scoped and immutable.
• D. Const is block-scoped and can be redeclared.

Answer: (B)

Understanding how those three declarations work hinges on scope and whether a binding can be reassigned. Var is function-scoped, so it belongs to the function it’s in, and it can be redeclared within the same scope. Let and const are block-scoped, meaning they follow the boundaries of blocks like those in if statements or loops. Let bindings are mutable, so you can reassign them. Const bindings are not reassigned after their initial value is set, though if the bound value is an object, its properties can still be changed. That combination of rules is why the statement that var is function-scoped and can be redeclared, while let and const are block-scoped with let being mutable and const being read-only bindings, is the best description. The other options mix up scope or mutability: var being block-scoped and not redeclarable, let being function-scoped and immutable, or const being redeclarable.

Understanding how those three declarations work hinges on scope and whether a binding can be reassigned. Var is function-scoped, so it belongs to the function it’s in, and it can be redeclared within the same scope. Let and const are block-scoped, meaning they follow the boundaries of blocks like those in if statements or loops. Let bindings are mutable, so you can reassign them. Const bindings are not reassigned after their initial value is set, though if the bound value is an object, its properties can still be changed.

That combination of rules is why the statement that var is function-scoped and can be redeclared, while let and const are block-scoped with let being mutable and const being read-only bindings, is the best description. The other options mix up scope or mutability: var being block-scoped and not redeclarable, let being function-scoped and immutable, or const being redeclarable.