One Pager Cheat Sheet

• A closure in Javascript is a feature that can be used to implement dependency injection, where a function can be passed in to access certain variables or methods.
• A closure is a combination of a function and a lexical environment in which it was declared, allowing the function to access its lexical environment even from outside of the outer function.
• Dependency injection with closures can be used to reduce coupling between an object and its dependency, while allowing reconfiguration without changing existing business logic, as an alternative to using global context dependencies.
• The logger remains encapsulated within the scope of createFactories and is accessible through the two returned child methods, emailFactory and smsFactory, all in O(1) constant time and space complexity.

This is our final solution.

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}

var assert = require('assert');

​

/*

 *  Closures

 */

var minus = (function () {

  var counter = 999;

  return function () {

    counter -= 1;

    return counter;

  };

})();

​

minus();

minus();

minus();

​

/*

 *  Dependency Injection With Closures

 */

function createFactories(logger) {

  return {

    emailFactory: function (greeting) {

      return function (greet) {

        logger(greeting + greet);

      };

    },

    smsFactory: function (text) {

      return function (text) {

        logger(text);

      };

    },

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