Old way of declaring variables Scope is function-based (not limited to blocks) Can be changed later Can be redeclared in the same scope Less safe and can lead to unexpected behavior Modern way to declare variables Scope is block-based Value can be changed (reassigned) Cannot be redeclared in the same scope Safer and more predictable than var const Modern way for fixed values Scope is block-based Value cannot be changed or reassigned Must be initialized when declared Used for values that should stay constant var → function scope let and const → block scope var is available before declaration but has an empty value initially let and const are also known before declaration but cannot be used before they are defined Default mode Less strict rules Allows unsafe or accidental behaviors Activated manually Prevents many common mistakes Safer and recommended for real projects