Question

What is module pattern in Javascript?

Answer 1

Module pattern is a designed pattern used to wrap a set of variables and functions together in a single scope returned as an object. JavaScript doesn't have access specifiers similar to other languages(Java, Python, etc) to provide private scope. It uses IIFE (Immediately invoked function expression) to allow for private scopes. i.e., a closure that protect variables and methods.

The module pattern looks like below,

(function () {
  // Private variables or functions goes here.

  return {
    // Return public variables or functions here.
  };
})();

Let's see an example of a module pattern for an employee with private and public access,

const createEmployee = (function () {
  // Private
  const name = "John";
  const department = "Sales";
  const getEmployeeName = () => name;
  const getDepartmentName = () => department;

  // Public
  return {
    name,
    department,
    getName: () => getEmployeeName(),
    getDepartment: () => getDepartmentName(),
  };
})();

console.log(createEmployee.name);
console.log(createEmployee.department);
console.log(createEmployee.getName());
console.log(createEmployee.getDepartment());

Note: It mimic the concepts of classes with private variables and methods.