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Implementing JavaScript creational patterns

From: Node.js Essential Training

Video: Implementing JavaScript creational patterns

While it's possible to get around module caching by using function scopes, it isn't the most flexible solution. In this video, we'll rework a module to generate objects. Let's start with the code from the previous video. Go to exercise files and chapter four, video three, and then copy the Start folder to the desktop. Now open the Start folder in a text editor. I'm going to go to Flight and index.js. In here, we have our current module, and it's exporting one function, and that function is creating a scope where we're holding all the variables.

Implementing JavaScript creational patterns

While it's possible to get around module caching by using function scopes, it isn't the most flexible solution. In this video, we'll rework a module to generate objects. Let's start with the code from the previous video. Go to exercise files and chapter four, video three, and then copy the Start folder to the desktop. Now open the Start folder in a text editor. I'm going to go to Flight and index.js. In here, we have our current module, and it's exporting one function, and that function is creating a scope where we're holding all the variables.

What I'd like to do is create another function that will serve as the base for new objects. Let's do that now. Make some space at the top and then type var Flight, with a capital F, equals function. Don't define any arguments for this function, and clean out the body. Notice that we're using a capital F for flight. This is just a reminder that we're using this as the base for new objects. Now let's start adapting our old code into this new function. First copy everything from line 7 to line 15, and paste it on line 2.

Now change it to this values. Instead of this values, I'm also going to change it to this data. Next, we're going to create a function that will perform what's currently happening on lines 25 through 29. I'm going to call this function fill. So copy lines 25 through 29 and then make some space in the flight function. And then define this.fill. Set this to a function, and have it take one argument. This argument will be named info.

Now paste in the code you copied a moment ago. Before we leave this function, one more thing we need to do is change values to this.data. Next, we need to pull in the old functions that we were returning previously. Go down to line 42 and copy everything from 42 to 50, and now paste all that on line 20. This time we're going to prefix all of the function names with this. And again we need to change values to this.data. Finally, we need to change the module exports function.

Clear out everything in the current function. So now what we want this module export's function to do is to create a new instance of the flight object. To do this, we're going to create a new variable. Start by typing Var. And I'm going to call this variable instance. And I'm going to set it to a new copy of flight. Next, I'm going to fill this new object with all the information that's getting passed in through the module exports function. And then finally, I'm going to return the instance.

After saving the file, let's go to terminal. Type in cd, and then I'm going to drag the start folder into terminal and that will give me the path. And if I list the directory contents I have app.js and flight. app.js is currently defining two different flights and it's outputting the first flight, then defining the second one, outputting it, and then outputting the first one again. So let's run this example. Type in node space app.js and then hit Return.

So this example is still returning separate instances for each flight, and this is exactly what we want. Now there's one thing to note about the function that we're exporting here, in index.js. This function may seem a bit redundant at first, but it's actually enforcing a consistent way of getting new objects. This extra function is serving as a factory. A factory is a design pattern for creating instances of objects. When you provide a factory, the end programmer doesn't have to think about how to set up an object, because the factory handles this.

It's also possible to return more than one type of object from a factory, based on whatever criteria you want. In the example here of a flight, we may want this factory to also return itineraries. It could detect if a destination is a string or an array, then return the right type of object based on that information. There may also be some scenarios where you really don't want to use a factory. In this case, you want to export the function itself rather than a factory function. I've included a no-factory version of both the app and the module in the Examples folder.

So in this example, instead of setting module exports to a function that acts as a factory, we're setting it to flight. Then in the application we're using the new operator to create new flight objects with that function. There are different ways of getting around module caching, depending on how you want to protect code and enforce consistency. Factories can streamline object creation and ensure separate instances on each call. In the next chapter, we'll start using the express framework to build an application.

In the meantime, I have a challenge in the next video, to help you get more hands on experience with modules.

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This video is part of

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Node.js Essential Training

52 video lessons · 13154 viewers

Joseph LeBlanc
Author

 
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  1. 3m 9s
    1. Welcome
      42s
    2. What you should know before watching this course
      57s
    3. Using the exercise files
      47s
    4. Using the challenges
      43s
  2. 18m 50s
    1. Why use Node.js?
      2m 1s
    2. Choosing a Node.js installation process
      4m 56s
    3. Installing Node.js on the Mac
      2m 5s
    4. Installing Node.js on Windows
      1m 43s
    5. Installing Node.js via Node Version Manager on Ubuntu Linux
      4m 45s
    6. Installing Node.js via Node Version Manager on a Mac
      3m 20s
  3. 13m 54s
    1. Exploring language additions to the V8 JavaScript engine
      3m 38s
    2. Understanding require() and modules
      6m 39s
    3. Understanding callback execution in the event loop
      3m 37s
  4. 12m 23s
    1. Initializing Node.js projects
      2m 37s
    2. Finding an NPM
      3m 30s
    3. Maintaining projects using the npm command
      6m 16s
  5. 21m 4s
    1. Creating modules with getters and setters
      6m 33s
    2. Understanding module caching and scopes
      6m 15s
    3. Implementing JavaScript creational patterns
      5m 8s
    4. Challenge: Leveraging module caching
      55s
    5. Solution: Leveraging module caching
      2m 13s
  6. 32m 27s
    1. Starting Express applications
      3m 42s
    2. Handling GET requests returning JSON
      3m 26s
    3. Navigating large datasets using request variables in routes
      5m 4s
    4. Modifying data through PUT requests
      4m 32s
    5. Supplying middleware to modify HTTP response headers
      4m 37s
    6. Generating HTML views in Jade
      8m 9s
    7. Challenge: List all records as JSON
      37s
    8. Solution: List all records as JSON
      2m 20s
  7. 25m 37s
    1. Evaluating unit testing methodologies
      3m 8s
    2. Isolating existing code for testing
      6m 47s
    3. Supplying helpers for test data
      2m 35s
    4. Writing unit tests with Mocha
      6m 5s
    5. Simulating HTTP requests with SuperTest
      7m 2s
  8. 28m 45s
    1. Connecting to MongoDB via Mongoose
      4m 16s
    2. Defining schemas for collections in Mongoose
      3m 47s
    3. Querying MongoDB collections
      5m 32s
    4. Persisting Express sessions through MongoDB and mongo-connect
      7m 6s
    5. Logging in to Express applications using Passport
      8m 4s
  9. 21m 47s
    1. Controlling the built-in REPL
      4m 18s
    2. Constructing a custom REPL
      5m 40s
    3. Receiving command-line arguments with Optimist
      6m 14s
    4. Building command-line tools
      3m 35s
    5. Challenge: Launch a custom REPL from a command
      41s
    6. Solution: Launch a custom REPL from a command
      1m 19s
  10. 15m 46s
    1. Emitting events and attaching listeners
      5m 32s
    2. Streaming chunked data through readable streams
      2m 33s
    3. Controlling readable streams
      1m 52s
    4. Piping readable data into writable streams
      2m 10s
    5. Handling duplex streams over TCP
      3m 39s
  11. 4m 6s
    1. Deploying projects to cloud hosting services
      2m 36s
    2. Finding Node.js resources
      1m 30s

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