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Hello everybody.

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Welcome back.

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And in this video, I want to show you something that got me really really really excited when I first started

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learning node, and hopefully you get just as excited as I am as we go through this video and then do

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a little bit of a challenge.

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It's going to blow your mind.

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At least it did for me when I first started learning to code.

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Now in the previous video we talked about something called the FS module that comes with node, and this

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is something that is built into node and the way we get it is we'll just do const.

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Well actually we need a file first, so let's do a touch script.js, we'll create a new script perfect.

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Alright we can close that because we don't need this.

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And in the script.js that we have in this folder or some node we can have 'const fs'.

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equals 'require('fs')', so FS here stands for file system and if you have node downloaded you have access

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to this.

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By just doing this.

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Now why is this so exciting and so useful.

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Well because FS file system allows you to access our file system, which again doesn't sound that exciting.

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But let me demonstrate what happens and why this is useful - so bear with me here.

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I'm going to do a bit of coding and then I'm going to explain exactly what is happening.

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So we're going to use the 'fs.readFile'.

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It's pretty self-explanatory.

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We have a blank parameter and then we have err for error, data.

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And this is an arrow function.

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So the second parameter is a function, and this function has either error or data.

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So for the error, I'm going to say if there is an error we'll just throw err, or we can just say console dot

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log errrroooorrr. Really shove it into their face.

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Alright! Now if there wasn't an error, we'll just say well we'll just say console.log and we'll just log out

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whatever data is.

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Alright.

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Let me add the semi-colons.

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And save that.

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So what I just do here. I just imported the FS module that comes with node and the FS module has a method

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readFile() that

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well it looks like it reads some sort of a file.

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The first parameter is actual file that we want to do, so the path to the file, which we don't have yet.

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So let's create one.

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I'm going to say new file and we'll call it 'hello.txt', and with 'hello.txt', we'll do our classic

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helllloooooo there!!!

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And exciting stuff so exclamation marks.

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We saved that and now we can say that we want to read the file.

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'hello.txt' from the current directory.

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Hello dot

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text.

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Now this readFile method is going to find the file with the path,

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ok, so here it is.

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It's going to read it and then if there's an error, it's going to spit out an error.

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If there's some sort of data and everything successful, it's going to spit out data. With the

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way we can run this file in node.

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Well well first I'll have to save it. We'll say node script.js

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Enter and I got buffer.

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What is that?

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And that is because we have to do a little bit of encoding.

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And what that means is if I do this 'toString()', let's just try this and show you what I mean.

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And I get.

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Hello there.

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So the 'readFile' reads the file as the name suggests, and it's going to spit out whatever it's reading.

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Data.

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Now why do we have to put in the 'toString()' here.

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Just so you know 'toString()' does something, by default if you don't add anything, it's going to use the

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encoding called UTF 8 and UTF 8 is a type of a coding.

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Let's just run this to make sure that this is still the same.

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Yep.

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So UTF 8 is a type of encoding that we have.

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That's pretty standard with HTML 5.

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And pretty much everybody uses it on the web.

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It's a way for us to have characters, whether they're Latin characters, you know ABC's or we have Korean

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Japanese, Chinese characters, they're all represented by a number, and UTF 8 is a way of encoding these

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numbers to make sure that we can read them.

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It's actually quite a complex subject, so I recommend the Wikipedia page that talks about UTF 8.

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For now just know that UTF 8 is a type of encoding that is pretty much standard across the web.

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You might have also seen ASCII and ASCII was before UTF 8 existed.

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ASCII was mainly for Latin based languages, so the ABCs; and UTF expanded that to include many more from

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many more languages from different parts of the world.

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Alright well a little bit of a tangent that we didn't need to go on, but as you can see over here we

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have

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'helllloooooo there' and we're able to read the file.

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Alright.

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Very cool.

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Let me just add one other method to your repertoire.

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Let's also do 'fs.readFileSync()' and 'fs.readFileSync()' works a little bit different than the previous

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one and sync stands for synchronous.

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So we'll see what happens.

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I'm going to put in

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'hello.txt' once again, and this time I'm just going to leave it like that.

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And let's just say that this is going to equal the file and we'll just 'console.log(file)'.

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Alright.

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Let me save that and run this.

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Alright.

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We know once again that we got this because we need to do 'toString()'.

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So let's do that.

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I'm going to try 'toString()'

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I'm going to save and run this again. Alright I get

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'helllloooooo there!!!'

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But just to distinguish them, let's just say that this is number one and this is number two.

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I save this, run this again.

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And whoa, what just happened.

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We have one coming after the two.

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Now if you've watched the asynchronous synchronous video in this course, then you might understand what's

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happening here.

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If not I'm going to do a quick synopsis.

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But I do recommend you check out that video. Now read file is asynchronous, and that's why it has something

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called the callback function.

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It is saying: hey I'm going to read this file, and when I'm done with it, you just keep going on with your

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business and keep reading.

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Line three, line four, line five, line six, all the way to 11.

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When I'm done, I'll let you know and I'll either give you an error or some data. 'readFileSync()' which

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is synchronous says: I'm going to read this file.

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Don't do anything, just wait here when I'm done

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I'm going to assign it to 'file' and then you can keep going.

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So as you can see here what happens is we read the file and because this is an asynchronous, it's going

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to run this and come to line 10 and run the 'fs.readFileSync()' and the 'readFileSync()' because it's saying

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hey wait until I'm done this, it is going to print out

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'helllloooooo there!!!'

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and then the asynchronous code is going to say: hey I finished reading the file,

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here's the data and it prints out down over here.

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Again I really really recommend you check out the asynchronous synchronous video.

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But for now hopefully that makes sense.

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Now looking at this, which one should you use? Well for a simple case like this,

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we can use whichever we want. But you may see a problem with the second one especially if we're building

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something like a server.

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If we have a massive file that has something more than 'helllloooooo there!!!',

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well if we're doing 'readFileSync()', what happens is we're going to halt or pause the execution of our

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file and it's going to read the entire text.

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And the program is just going to be waiting for that to finish; versus the read file which says: hey you

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can keep going ahead.

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I'll let you know when I'm done with this.

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So when you're building a server and let's say an express server with routes.

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Well in that case we want to use readFile() if we're reading any sort of a file or text file, whatever

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it is.

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Because that way we're not blocking the execution and the program can keep doing things.

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Alright.

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So one last time just to clarify things.

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I'm going to label this as 'Async' and 'Sync'.

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So once again if we run this we have 'Sync' and 'Async'.

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'helllloooooo there!!!'

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But very cool we're able to read a file and both instances which was kind of cool.

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Let me show you a few more of these and then tell you exactly why this is so exciting, and how we can

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use it to do some really exciting things.

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So let's say the 'helllloooooo there!!!' text is kind of boring and we want to add to it.

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Well we can do something like this.

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'fs.appendFile()' we give it the file we want to append.

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So in this case it's './hello.txt'.

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And by the way if this doesn't exist, it'll actually just create the file for us.

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And the second parameter will say what we want to add.

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So let's say we also wanted to add maybe a space and then say "This is so cool", now there is an exclamation mark.

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And finally third parameter takes in an error and this error will just say that if there is an error.

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Let me make this smaller

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so you can see - let's just say if there is an error, we'll just 'console.log'

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'console.log(err)'

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Alright.

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Perfect.

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So let's run this and see what happens.

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I'm going to run the script and I get

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'helllloooooo there!!!'

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'helllloooooo there!!!'

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Because these ran first but if I go to 'hello.txt', look at that, we just wrote to a file. And now we have "This

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is so cool."

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So if I run this again and let me clear this just so we have more space

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Look at that. I get

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'helllloooooo there!!!'

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'This is so cool'

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'helllloooooo there!!!'

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'This is so cool'

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If we go back to the hello.txt file, Oh boy we've add in even more

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'This is so cool'

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text.

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So that's pretty cool.

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We just added a few more lines to our file.

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Let me remove that just so it doesn't get too annoying.

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Going to save it and come back.

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All right so we learned the append.

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Let me just comment this out so that it doesn't interfere with any of the other ones.

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Let's do a 'write' this time - now create some space here so we can see

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With the write, as you can imagine,

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'fs.writeFile()' and we'll just say that this file will be called 'bye.txt'.

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Very original naming by myself.

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And will just say.

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Sad to see you go.

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And once again it'll take an error and this error will say 'if (err)' 'console.log(err)'

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Alright, so let's save that, run the file or run the script.

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And look at that, 'bye.txt' just got added.

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If we click on it, we have "Sad to see you go".

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We've just created a new text file.

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Very very cool.

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By the way, just so you know what happens, if let's say I misspell the read file and now it's 'hell.txt'

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Well if I run this, I'll get an error and you can see that.

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Because it errors out I get the error message, error with a lot of R's.

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Alright.

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A little bit of a segue there but just in case people are asking or you were thinking about that.

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Alright.

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Woo~ I'm getting tired so let's do one last one and then I'm going to tell you exactly why this is so

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cool.

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The final one we're going to do - again let's make some space here - is going to be the 'delete'.

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So with that 'delete' we can do 'fs.unlink()'.

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the name is a little bit off here but 'fs.unlink()' and we'll say the 'bye.txt' and notice that I was able to

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just do 'bye.txt' but just to keep it consistent, I'll just say './bye.txt' with the './' before

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it

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and with this one.

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Again if there's any errors

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just 'console.log(err)'

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Whoops I forgot to do the 'if'

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perfect, now

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Well let's see what happens here.

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And just for fun, let's just add a 'console.log()' here after it has done deleting and we'll say 'inception' because

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we're saying 'bye' to the './bye.text'. Mind blown.

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Alright let's run this.

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I'm going to say - and we'll comment out the write file here because you don't need to write it,

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we already have the 'bye.text'.

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Let me save.

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Now if you look at the 'bye.text', let's see what happens here when I run the script

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look at that, the 'bye.text' was just removed.

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Inception just happened.

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Awesome.

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So that was very exciting for me hopefully it was for you as well.

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But why is this exciting?

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Well because now we're able to use programming in javascript outside of just web browsers and outside

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of just building websites and servers.

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What we can do now with this knowledge is we can make our lives easier.

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You can think of cases maybe you want to read an excel file and there are things that you can use, using

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read file and using NPM modules that you can read.

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Let's say.

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Columns in an excel and do some math.

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Or maybe you have an excel sheet with all these emails and you want to send out an e-mail to let's say

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100 people on this list but you also don't want to be caught spamming people by the google filter saying

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that hey this account is spamming because they just sent 100 emails in two minutes. Well using something

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like Node, you can create perhaps something that in every six hours, sends out five e-mails.

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Another thing you can do if you had a robot for example something similar to a file system instead of

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having reading from the file.

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You can read from the robot, maybe through wireless maybe through wires and get an input of some data

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that the robot has.

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Maybe it detected a cat.

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Well using that input, you can do something you can respond maybe send you an e-mail saying that the

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robot just detected a cat and send that e-mail out or send an output.

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And that's what we call input output, where you're getting an input from another source, another machine

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and then you are also outputting something for consumption, that is really really exciting because it

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opens up the world where you can create tools for yourself.

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You can automate things.

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You can literally do anything that your mind can think of.

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And I know this is still early and you're still at the beginning of your developer career but this is

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the first step into understanding how you can use programming to solve problems and make your life

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more efficient, or maybe just a little bit more fun.

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So in the next video we're going to do something fun.

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We're going to use what we've just learned and we're going to help Santa out on a coding challenge.

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I'll see you in that one.

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Bye-Bye