Scope

Example 1

Block scope does not work with Javascript when using the var keyword.

if (true) {
  var myVal = 'Hello World!!';
}

console.log(myVal);

This will print the myVal, even though the myVal is inside the block scope.

Example 2

Functional scope works with the var keyword.

function myMethod() {
  var myVal = 'Hello World!!';
}

console.log(myVal);

Now the myVal is inside the functional scope. This is not accessible from the global lexical environment.

Example 3

To use this block scope, instead of using var keyword, we can use const or let keyword.

if (true) {
  const myVal = 'Hello World!!';
}

console.log(myVal);

if (true) {
  const myVal = 'Hello World!!';
}

console.log(myVal);

In the both example the JS engine will through the Reference Error.