How do you declare a namespace?

Even though JavaScript lacks namespaces, we can use Objects, an IIFE (Immediately Invoked Function Expression) or let/const to create namespaces.

1. Using Object Literal Notation: Let's wrap variables and functions inside an Object literal which acts as a namespace. After that you can access them using object notation

         var namespaceOne = {
             function func1() {
                 console.log("This is a first definition");
             }
         }
         var namespaceTwo = {
               function func1() {
                   console.log("This is a second definition");
               }
           }
         namespaceOne.func1(); // This is a first definition
         namespaceTwo.func1(); // This is a second definition
         

1. Using IIFE (Immediately invoked function expression): The outer pair of parentheses of IIFE creates a local scope for all the code inside of it and makes the anonymous function a function expression. Due to that, you can create the same function in two different function expressions to act as a namespace.

         (function () {
           function fun1() {
             console.log("This is a first definition");
           }
           fun1();
         })();

         (function () {
           function fun1() {
             console.log("This is a second definition");
           }
           fun1();
         })();
         

1. Using a block and a let/const declaration: In ECMAScript 6, you can simply use a block and a let declaration to restrict the scope of a variable to a block.

         {
           let myFunction = function fun1() {
             console.log("This is a first definition");
           };
           myFunction();
         }
         //myFunction(): ReferenceError: myFunction is not defined.

         {
           let myFunction = function fun1() {
             console.log("This is a second definition");
           };
           myFunction();
         }
         //myFunction(): ReferenceError: myFunction is not defined.