Q296: How do you declare a namespace - JavaScript Internals (521 Qs)

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

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

javascript

     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

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.

javascript

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

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

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.

javascript

     {
       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.