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When you install Node, it already comes bundled with a whole bunch of built in modules.
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These are essentially libraries of code that the Node team wrote so that they can help you with day to
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day things that you might want to do using Node.
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Now, we mentioned that by liberating Javascript from the browser using Node, we can now use Node.js to interact
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with the computer directly.
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So a good example of that is we can use Node.js to get access directly to the local files of the computer.
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So let's take a look at one of the built in modules for Node that helps us to do that.
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So if you head over to nodejs.org/api, then you can see all of the native modules and the documentation
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of how you can use it.
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Now if we have a look in the left hand bar here, there's something called the file system.
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And, as you might predict, this helps you interact with the local file system using Node.
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Now there's a whole bunch of methods and properties that you can tap into, but in order to use the module
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we first have to require it.
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Now if we head over to Atom and add that new project folder that we created earlier on into our sidebar,
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so intro-to-node, and we can delete our console.log in our index.js. Now instead of having that,
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we're going to use the file system module, and we're going to write this line of code in order to use
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this module.
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So the first thing we write is a keyword called const, and up till now we've not been using this keyword
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at all.
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We've been using something called var.
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Now var creates a variable where, say, for example, if I said var a = 2, then later on I decide to
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change the value of a, a now equals 5, then this is how you can use vars to vary your variable.
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Now const stands for constant,
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and if I create a constant and I assign it a value, later on I can't change the value.
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I can't then say a now equals 5.
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It'll actually give me an error, and it'll tell me that attempting to override a,
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which is a constant.
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That means that once you've assigned it a value, you can't change constants any more.
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And this is useful when you're creating containers that are not going to be changed or meddled with later
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on.
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So, for example, if in my web site I needed to use the value of pi, then pi is never going to change, right?
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So I might just create a constant called pi and set it to 3.14159, and that's about all
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I can remember.
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So, in this case, we're creating a const called fs, and that stands for file system.
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Now you can call this constant whatever you want. You can call it fileSystem. But for simplicity's sake we're
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just going to call it fs. And we're going to set it to equal the file system module. And in order to use
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libraries of code, or modules, or packages, inside our project, we have to require the module. And the module
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is called fs.
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So let's go ahead and add that in here.
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So here's our brand new constant called fs, and it is set to equal the module that is fs. And we get access
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to it
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using this require method from Node.
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Now, at the moment Atom is giving me a warning here,
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as you can see from this little yellow dot, and it's telling me that the JSHint package, that I installed
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to keep my Javascript code tidy and consistent with other programmers, is giving me a warning saying that
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const is only available in ES6, it’s the latest stable version of Javascript at the time of recording.
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And I can switch off these warnings by simply writing a comment that says jshint
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esversion:6,
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and this will tell the linter that I'm actually using ES Version 6,
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don’t worry about the weird syntax,
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this is simply a new feature of our
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ES
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Version 6 of Javascript.
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So now that we've required fs, that means that we've incorporated this file system module into our project,
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and we're now able to use it in our project.
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Now, what are the sort of things that you can do using file system?
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Well, there's actually a whole bunch of things that you can do,
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for example, you can specify paths, you can open files, you can change files, you can access and read and
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write to the local file system.
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But, as we said before, we should be able to access and manipulate the local files if we're using Node.js.
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So let's just use one of these methods to show you that this is possible.
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So inside my intro-to-node, I'm going to create a new file, and I'm going to call it file1.txt.
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So this is just a pure simple text file.
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And inside here I'm just going to write a little bit of text,
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“I am file 1.”, hit save,
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and now I'm going to go into my index.js, and
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I'm going to use this method called copyFileSync in order to create a copy of my file,
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file1.
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So our docs will tell us how to use it, and what we have to do is first, of course, require the module,
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and then we're going to call the method and we're going to pass in two parameters.
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So the first parameter is the source,
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so that's the source filename to copy.
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And the second one is the destination, which is the destination filename to copy to.
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So that seems pretty easy.
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So all you have to do is say fs.copyFileSync, and the source file is called file1.txt, and the destination
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file,
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we’ll just call it file2.txt.
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So, what this line of code will do is look within the current directory,
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so intro-to-node folder, it will look for a file that's called file1.txt, and then it will copy
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it to something called file2.txt.
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Now currently file2.txt doesn't exist.
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So this is going to be the name of our copy.
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So now if I hit save and I head over to Hyper, and make sure that you’re still within the directory that
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our index.js is contained, which I've previously called intro-to-node.
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Now here I'm going to use the node command, and then I'm going to run the index.js file using Node.js.
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So now that I see my prompt again, so my name plus the dollar sign,
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that means that this execution has completed.
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So now, if we head into Atom and we look inside our folder, intro-to-node, you can see I now have two files,
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file1, which still has the same content as before, and also file2, which now has the copied content
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from file1. So if file2 already existed, then this copyFileSync will simply replace the existing content.
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So, let's say that in file2 we have some text saying that “I am file 2.txt” and we hit save, and we
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run our script again,
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then it will again try to replace what's inside file2 with a copy of what's inside file1.
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So file2 currently reads “I am file 2.txt”.
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So, in order to run the last command, all you have to do is just hit the Up key on your keyboard, and
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it will,
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and you can cycle through all the previous commands that you've entered.
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And this is just a quicker way of repeating commands.
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So we're going to run that file again,
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and now it's done.
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And let's head over here.
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So file2 now reads “I am file 1.” It’s cool, right?
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So we're able to use Node.js to write Javascript code and execute it to affect our computer, including
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manipulating and reading and writing to our local file system.
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Now in the next module, we're going to talk about how we can use external modules,
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so not just the modules that come bundled with Node, which are available here,
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but actually there's a whole bunch of libraries that other people have written which we can tap into,
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and we can use, using something called NPM.
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So for all of that and more, I’ll see you on the next lesson.