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• const — constant. block-scoped. You can't assign a new value to a constant, although if constant is an object or an array you can change its properties and items.
• let — block-scoped. It exists only in current and descendant scopes.
• var — not block-scoped. It seems people avoid using var in modern JS.

function () {
    for (let l = 0;) {} // will be available inside the loop only
    for (var v = 0;) {} // will be available outside the loop and inside the function scope

console.log(l) // l is not defined
console.log(v) // shows value of v after for is finished
}
const c = 0;
c = 2; // Error