Closures

A closure or “block scope” defines variables in a scope with curly braces and these and do not persist out the scope.

Approaches

For loop

See Looping section.

If else

See Control flow section.

Functions

See Functions section.

Any plain block

Defining a constant variable in a scope.

{
    const x = 1
    console.log(x)
    // 1
}

console.log(x)
// Uncaught ReferenceError: x is not defined

Defining a variable in the outer scope, overriding it in the inner scope and then using the outer one again.

let x = 1

{
    x = 2
    console.log(x)
    // 2
}

console.log(x)
// 1

Scoping a variable