Design Patterns (JS)

Question 1

Pattern to solve the problem of having service layers

Answer 1

module pattern

Question 2

pattern for overly complicated object interfaces

Answer 2

facade pattern

Question 3

pattern for better visibility into state changes

Answer 3

observer pattern

Question 4

types of patterns

Answer 4

creational
structural
behavioural

Question 5

creational patterns

Answer 5

Constructor (js specific)
Module (js specific)
Factory
Singleton

Question 6

structural patterns

Answer 6

Decorator
Facade
Flyweight

Question 7

behavioural patterns

Answer 7

Command
Mediator
Observer

Question 8

Ways to create an Object

Answer 8

var newObj = {};
var newObj = Object.create(Object.prototype); // will come up around inheritance
var newObj = new Object(); // a little out of favor, use class instead

Question 9

Ways of assigning value to objects

Answer 9

. notation
obj.param = ‘new value’

[] notation
obj[‘param’] = ‘new value’ //one big benefit is being able to use variables inside []

Question 10

defineProperty on object allows to…

Answer 10

add some additional settings to the objects properties, for example if it can be enumerated, configured or writeable

Object.defineProperty (object, ‘param’,{
value: whatevervalue,
writable: false, //can’t overwrite this later with object.param assignment
enumerable: false //won’t be listed among the params of the object
configurable: false //won’t allow later defineProperty amendments
})

Question 11

Inherit an object from another object

Answer 11

var obj1 = {whatever};

var obj2 = Object.create(obj1) //copies obj1

Question 12

Constructor pattern is used to

Answer 12

create new objects with their own object scope

Question 13

What happens when you put “new” in front of the function

Answer 13

Creates a constructor function: a new object, links to an object prototype, binds “this” to the object scope, returns “this”

Question 14

Create prototype of the object

Answer 14

ObjectName.prototype.methodName = function…

Question 15

Why use prototype?

Answer 15

To abstract large functions and avoid repeating them every time we create a new instance of the object. Prototype allows to reference these chunky pieces of code in one place without creating a copy of them with each new instance of the object.

Question 16

Module pattern in a nutshell

Answer 16

Simple way to encapsulate Methods

Creates a “Toolbox” of functions to use

Question 17

A module pattern at its core is just ____

Answer 17

an object literal

Question 18

Unlike a Constructor, Module is rarely ____

Answer 18

copied or needed more than 1 instance

Question 19

With Module, we can abstract out ___ work

Answer 19

db

Question 20

Best practice with defining methods in Module

Answer 20

Declare at the top, then reference at the bottom for readability

Question 21

Using Constructor and Module together

Answer 21

Create a Module which accesses data in db, and pass that to an instance of constructor that takes the DB data and creates new object

Question 22

Factory pattern is used for…

Answer 22

Simplifying object creation
Creating different objects based on need
Repository creation

Question 23

Singleton pattern is used for…

Answer 23

restricting an object to one instance of that object across the app

Question 24

How does the Singleton work…

Answer 24

Remembers the last time you used it

Hands the same instance back

Question 25

Structural patterns deal with…

Answer 25

relationships of objects - either extend or simplify the functionality

Question 26

Decorator pattern is used for ….

Answer 26

adding new functionality to existing object, without being obtrusive

Question 27

Decorator pattern allows for (4)…

Answer 27

more complete inheritance
wrap an object
protect existing object
adding extended functionality

Question 28

Facade patterns is used to…

Answer 28

provide a simple interface to a complicated system. jQuery is the best example of Facade implementation

Question 29

Flyweight pattern is used to…

Answer 29

conserve memory by sharing portions of an object between objects. only useful if you have large number of objects, or if the objects are large (but few)

Question 30

Behavioural patterns are concerned with

Answer 30

the communication between objects and the assignment of responsibilities.

Help objects cooperate.
Assign clear hierarchy.
Encapsulate requests.

Question 31

Observer pattern allows to…

Answer 31

allows for a collection of objects to watch an object and be notified of changes

Question 32

Why Observer?

Answer 32

Allows for a loosely coupled system

One object is the focal point (a little coupled)

Question 33

How does Observer work (example of Task)

Answer 33

Task is the Subject

Logging, Notification & Auditing are observer services
task has ObserverList{} and Notify() function that calls functions within observers

Question 34

example structure of files for Task (Observer)

Answer 34

task. js that contains task code
main. js that start with the following:

var Task = require(‘./task’);

then create Observers within main.js

then create the ObserverList

Question 35

Mediator pattern…

Answer 35

controls communication between objects so neither obj has to be coupled with others

Question 36

Mediator allows for

Answer 36

loosely coupled system
one object manages all comms
many to many relationship

Question 37

Command pattern is …

Answer 37

encapsulating the calling of a method as an object

Question 38

use Command pattern to…

Answer 38

fully decouple the execution from implementation
much less fragile implementations
supports undo operations
supports auditing and logging of operations

Question 39

.call vs .apply

Answer 39

apply allows to pass in an array of args

call requires to state each arg

Question 40

make a list of arguments that come after the first argument

Answer 40

var args = Array.prototype.slice.call(arguments, 1)
[].slice.call(arguments,1) //simplified version