feat(Shadowing): Shadowing in JavaScript

Signed-off-by: cankush625 <cankush625@gmail.com>

Author: cankush625

Advance/shadowing.js

@@ -0,0 +1,51 @@
+// Shadowing - If the variable is defined outside the block with the 
+// same name then the variable inside the block shadows the variable outside the block.
+
+// Shadowing in Block Scope
+// This is the valid shadowing
+var num = 10;
+let digit = 5;
+// Block Scope
+{
+    var num = 20;
+    let digit = 7;
+    console.log(num); // 20
+    console.log(digit); // 7
+}
+console.log(num); // 20
+console.log(digit); // 5
+
+// Shadowing in Function Scope
+var username = "ankush";
+let rank = 1;
+function myName() {
+    var username = "roshan";
+    let rank = 2;
+    console.log(username); // roshan
+    console.log(rank); // 2
+}
+myName();
+console.log(username); // ankush
+console.log(rank); // 1
+
+// Illegal Shadowing
+// let a = 20;
+// {
+//     var a = 40;
+// }
+
+// Legal Shadowing
+// let a = 20;
+// function sum() {
+//     var a = 40;
+// }
+
+// let a = 20;
+// {
+//     let a = 40;
+// }
+
+// var a = 20;
+// {
+//     let a = 40;
+// }