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Receiving command-line arguments with Optimist

From: Node.js Essential Training

Video: Receiving command-line arguments with Optimist

Every time we've run a Node program, we've done it from the command line. It will be very convenient to be able to configure our program, as we run it by specifying some command line arguments. Node provides tools we can use to do that. In this video, we'll write some code accepting command line arguments. First let's go to the Exercise Files and set up the project. Go to chapter 8 and video 3, and then Copy the Start folder onto the Desktop. Next go to Terminal, and change directory to that folder.

Receiving command-line arguments with Optimist

Every time we've run a Node program, we've done it from the command line. It will be very convenient to be able to configure our program, as we run it by specifying some command line arguments. Node provides tools we can use to do that. In this video, we'll write some code accepting command line arguments. First let's go to the Exercise Files and set up the project. Go to chapter 8 and video 3, and then Copy the Start folder onto the Desktop. Next go to Terminal, and change directory to that folder.

I'm just going to drag it in to get the path. Then press Return, and then type npm space install. And also follow that by Return. So once that's complete, open up the Start folder in your Text Editor, and first let's go to server.js. Now Node is already keeping track of what's being entered on the command line, and it's actually pretty easy to get to. Let's see what Node keeps track of. Type in console log and then process.argv. So now, let's go to terminal and start up the server.

I'm going to type in node space server, and now I'm going to pass in some arguments that I'd like to use in a moment. But for now we're just going to see how they come through in Node. So first I'm going to pass in flight as a flag. So dash, dash flight, and the number's going to be 567. And then another flag for destination. And I'm going to provide LAX as the value for that. So now press Return, and you'll see here that it comes back as an array. The first item is Node itself, and then the second item is the path to the file that's being run.

And then the remaining items are the flags and values that we passed. So this is great. We have access to all this data, but there's a bit of a problem. You notice we're getting an array here of arguments. This is nice, but it's still going to be a pain to pick through. It'd be much more helpful, if we could get this data back in an object, where we can look up the values by Property. It turns out the Node community provides several modules for doing just that. I'm going to install one of them named optimist.

So first I'm going to stop this server. I'm going to press Ctrl+C, and now I'm going to install optimist. Type npm install, and them dash, dash save. And then optimist. So now optimist has been saved and installed. Let's add it to our application. Go back to server.js, and now in the list of variables that get included, we're going to require optimist. We're going to set a new variable called argv, and we're going to require optimist.

And we're actually going to read the argv property from optimist. And then we're going to finish that with a comma. So now let's inspect that argv variable. Type in console log, and argv. So now we're going to compare what optimist gives us, with what we get from the process from node. To Save the file, and let's go back to the command line. I'm going to press up two times. And that's going to give me, node server --flight 567 and --destination LAX. And now when I press Return, I now get two items.

The first item, is the object that we get from optimist, and the second item is the array that we're getting from the process. So notice here, that the different flags are coming through as properties. So we have a property for flight, and the value is 567. And we have a property for destination, and the value is LAX. We also have another property called dollar sign zero, and that's showing us the command that was used to run this script. So this is exactly what I want. I now have an object, that has all the properties and values that are getting supplied on the command line.

So now let's use those values in our code. I'm going to stop this server by pressing Ctrl+C, and and now I'm going to go back to server.js. So now I'm going to get rid of both lines 11 and 12, because I don't need them anymore. And now I'm going to add some logic for handling argv. So what I want to do is make sure that flight and destination are both set, before doing anything with those values. If destination is set, that doesn't really tell me anything, because I need to know which flight to set the destination on.

So, let's do an if statement, and test to make sure that argv flight is set. And let's also make sure that argv destination is set. So if both of those properties are set, I'm going to set this data in the flight. So first we're going to look up that flight, by flight number. And then we're going to set the destination property of the data in that flight. So I'm going to press dot and then data, and then destination, and then I'm going to set that property to the value of argv destination.

So now I'm saving the file. First, let's go to the server and let's just start the server with no command line arguments. I'm just going to go node space server. And press Return. And now I'm going to go to the browser, and load up localhost at flight 567. So, at the moment, the destination is Denver. Now, let's try restarting the server with some command line arguments. I'm going to press Ctrl+C to stop the server. And then I'm going to press up two times. And that's going to get me the command line arguments, that I typed in earlier.

So, now I'm going to press Return. And, now it's saying that data is not defined. There's a slight problem with the logic in my code, and I'm going to fix that. So, let's go back to the Text Editor. Turns out, the name of the variable that's holding the data is actually flights. So, I'm going to change data to flights. Save the file. And now I'm going to press up to get that command again, and press Return, and now it says, the Express server is listeing on port 3000. So I can go back to web browser and hit Refresh, and now the destination is set to LAX.

Modifying an application to receive command line arguments, is made easier through the use of modules like Optimist. Optimist provides a convenient object containing everything from the command line. In the next video, we'll build a complete Command Line tool.

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This video is part of

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Node.js Essential Training

52 video lessons · 12362 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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