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All right welcome back and this video we're finally going to talk about what the dash dash to save flag

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means when we do NPM install.

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I had initially intended for this to be at the end of the last video but because of time constraints

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as I started recording this I realized that there was some more detail that we needed to talk about

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and a few other components that I wanted to bring into the discussion and that it made sense for it

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to be a standalone video.

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So the objectives here are to use the dash dash save flag to install packages and understand what it

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means.

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Explain what the package that Jason filed does and then use another command.

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NPM and knit to create a new package.

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Let's start by talking about this file package Scott J song.

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And to do that I'm going to open up a nice blog post on the blog of a company called Noj it too and

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this post explains what the package that just on file is every single NPM package that we've used and

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that we will use in the future has a file called package J song.

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So I can show you that first if we look at our first express app and we look in the Express directory

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there is a file called package that Jason and we're going to discuss Jason later on.

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It stands for a javascript object notation.

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It's just a data type is a way of formatting text in a file to represent structure.

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And what this is is a file that contains all the meta data about this particular application or this

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package express so it contains a description a name an author and then all the different contributors

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who have added to it.

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It also contains the license the get hub repository you are l the homepage so it can be used to search

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for it and probably most importantly the dependencies.

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These are all the packages that express relies on that it needs in order to work.

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And there is quite a few of them as you can see here.

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And this file will collect them all.

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And also explains the versions that are needed.

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So that's what the package that some file is it holds metadata relevant to a specific project and I'll

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show you one more example.

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This is actually the same package that Jason but this one is on get help.

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It's on the Express repository.

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So this is the Express code itself being hosted on get help.

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And we have a package such a song and inside of that here's all the same data that we just saw.

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But the reason I'm showing it to you is that you might notice that the node modules directory is actually

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not included it's not on get help but it is included when we go and look at Express right here instead

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of Express we have lib and node modules and then package stuff Jason and a few other things I don't

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get how there's just lib and node modules.

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It's nowhere to be found.

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And that's for a very particular reason which is that when we're sharing code and packages and repositories

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are big projects and they depend on 10 20 or even 100 other packages rather than uploading all of these

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packages with the rest of our code we can just put them in the package store J song.

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And then when someone installs Express and someone downloads this or fork's this repository it makes

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their own copy.

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And they want to use it.

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They'll see what they need to install but they won't download all of the baggage that goes along with

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this automatically.

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Luckily there's also a really easy command to automatically install everything inside the package such

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Esan under dependencies and we'll also see that later on I came up with a silly analogy to help explain

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this idea of the pack.

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Jaison and in particular the dependency section.

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So imagine that you have a great recipe a great dish that you make and I want my friend in Denmark to

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be able to replicate the meal that I can make here in California.

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So one option would be for me to go buy all of the ingredients for him package them all up pre-measured

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everything put it in Ziploc bags and then put everything in a big box add in some instructions on how

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to cook them.

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Throw in some instructions on how to cook the meal.

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Tape it all up and then go to the post office and pay a lot of money to ship it to my friend in Denmark

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.

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The alternative is just to send my friend a letter.

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And in that letter we'll just describe the ingredients and the quantities that are needed.

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And then once that letter gets to Denmark my friend can figure out what he needs to buy what he already

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has how much he needs everything and he can prepare the meal on his own.

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Hopefully you can see where I'm going with this.

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The way that the package that Jason works is that it's the recipe for the ingredients that are needed

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for a specific package or library rather than sending the contents of all of these individual packages

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.

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We just send a package that Jason that is basically a shopping list for all the packages and whoever's

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using that package can then easily go and install all of these sort of up all that up.

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Peggy Stut Jaison contains a bunch of metadata about a particular application or package and that ranges

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from things like the name of it the description of version number all the way down to the dependencies

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which in my mind is the most important aspect.

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It contains a list of packages and the version number of each package that's needed in order for this

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application to run.

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So that brings me to the next point which is what does a dash dash save do.

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When we install a package with NPM install and we add on this flag at the end.

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Dash dash save it will take the package name and version in automatically save it into our package JS

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on file if we have one.

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Oh quickly demonstrate that we are to make a new directory and I'm just going to call this package.

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On demo and then CD into that.

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And the first thing I need to do is create a package that JS on file and I can do that myself by doing

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touch package that Jason and then filling out all those fields.

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But there's an easier way which is this third little bullet point here using NPM and need to create

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a package Duguay some for us.

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So go down to my terminal and type NPM in it inside of the folder where I want my application to exist

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in this case package based on demo.

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I'll hit enter and I get this message printed out to me.

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It says this utility will walk you through creating a package dot JSON file.

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Basically it asks me a bunch of questions like what's the name of my package.

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And then I type it in and then hit Enter when I'm done and we'll ask me another question and then we

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use all that data to make our package that Jason at the very end.

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So for name it's guessing that we want to call it package to chase on demo because that's the name of

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the folder we're in.

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Which is fine.

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So we can just hit enter and it will use that.

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Same thing with version if I just hit enter it will use version 1.0 0.00 does need to be in this format

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of some number.

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Another number another number description.

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Well just do simple package that J some demo entry point refers to the file where application starts

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and in most of our applications it's going to be apt.

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Yes.

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And that's just a personal preference in this case.

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We're not really going to have an application at all.

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We're just installing packages just to show you how it works.

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So we can put whatever we want we'll hit enter from test command and get repository keywords as well

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.

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We're not going to enter any of that for author can put in cold steel license and just use the default

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one and you can see it shows me a little preview of what it's going to do and then it.

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Is that OK.

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I'll get yes or enter.

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And now if I type LS I have a new file package such a song.

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So here's the package that Jason move it up here you can see it has our name and our version and everything

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else that we did.

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But it doesn't have any dependencies yet.

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So now let's go and install a new package will do express.

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So we just run NPM install express and then dash dash save at the end and hit enter.

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And you see we now end up with a dependancies field here and it has.

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EXPRESS And then our version 4.1 3.3.

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And we can install another package like Cat me dash dash save and it adds that into Pakistan based on

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under dependencies as well.

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All right so let's wrap up the package.

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Jason file contains metadata about an application order package.

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It's really really common to see them and really common for us to create our own package that Jaison

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using NPM in it for every single app we make from here on out every single real app.

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That's not just a quick demonstration.

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We'll be using NPM in it and creating a package that Jaison.

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And the last important point is that we can use dash dash save when we're installing a package.

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Doesn't matter what package any package we just add dash dash save at the end.

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And that will install it and then also save it to the dependency section of our package that Jason along

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with the version that we installed.

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OK.

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In the next video we're going to keep moving forward with Express