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

2. 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();
})();

3. 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.