Const keyword means constant, a value that won’t change after the application has been compiled; this allows for certain optimizations.

JavaScript does not have compile-time constants (it’s usually not compiled after all). The const keyword declares an immutable variable.

Let keyword is a JavaScript variable that is safely scoped down to the method or function level.

Variables declared with let are scoped to the block, not to the function.

Var keyword is generally discouraged in JavaScript, because it’s a global declaration. The value of it could be available anywhere in the application, and the app might have collisions.

var is scoped to the function, not globally (unless it’s at the global level). It is discouraged because of its confusing semantics (“variable hoisting”).