JavaScript provides three ways to declare variables: var, let, and const. While var is function-scoped and allows redeclaration, let and const were introduced in ES6 and provide block scoping, with additional restrictions to enhance code clarity and reduce bugs.

var is function-scoped and allows re-declaration and reassignment. It can leak outside of block-level code.

let is block-scoped and does not allow re-declaration in the same block, but reassignment is allowed.

const is block-scoped and does not allow re-declaration or reassignment. It must be initialized during declaration.

var is function- or globally-scoped, while let and const are block-scoped.

var is either globally scoped or function scoped. It is accessible outside of block statements like if, for, etc.

let is block-scoped. It cannot be accessed outside the block in which it's defined.

const is also block-scoped like let. It cannot be accessed outside its defining block.