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[MUSIC]
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So far, we have been making use of
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Visual Studio Code's auto-import feature to import
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the various files and packages that we've been
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using throughout our application so far.
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If we take a brief moment here to actually
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inspect some of the imports that we have,
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for example, I'm within our movie model right now,
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we'll see something that we might not be familiar with,
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this hash services/cache service.
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Particularly, it's the hash services
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portion that you may not be familiar with.
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However, as we hover over this particular import,
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we see that Visual Studio Code is successfully able to map
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this back to a module at our code,
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let's learn AdonisJS 6 at services/cache service file,
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which is absolutely correct.
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We go at services/cache service,
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and that is indeed the file that we're importing here.
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So how exactly is that mapping happening?
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That's what we want to discuss here today.
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So this is using a feature called Node.js subpath imports.
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If we dive into the documentation here,
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so let's open up our browser and head to
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nodejs.org/api/packages.html/subpathimports.
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There's a whole section here talking about what these are.
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If we go ahead and scroll down here a little bit further,
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we'll see subpath patterns.
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This is the particular feature that AdonisJS
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is making use of to allow us to specify that hash services
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to then import from our app services directory.
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Within the example here,
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we see that we have an imports object,
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which has a mapping of hash internal/star.js.
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The hash internal is defining a subpath import namespace.
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The star is allowing us to specify any file
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within the internal directory
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that we're in turn pointing to right here.
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And then the .js is required
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because we're working with ECMAScript modules,
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so we need to specify the file extension.
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The right-hand side of that is then pointing
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to the underlying directory and the files therein
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that our import namespace should resolve to.
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So if we were to specify an import for hash internals/test.js,
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the underlying file would wanna be within
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source internal/test.js.
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If we scroll down just slightly further,
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Node.js will describe this within their documentation.
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So you have an import for various features
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from es-module-package/features/x.js,
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and then they'll have the underlying resolved package
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from that import right here.
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If we scroll up a little bit further,
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they also describe why the hash is there.
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So right here, entries in the imports field
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must always start with a hash
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to ensure that they are disambiguated
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from external package specifiers.
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Essentially meaning it's a special character
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that allows them to know specifically
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that you wanna use a subpath import
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to import the particular file that you're working with,
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as opposed to like the at or ./ designation
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that you could be doing to import from Node.js
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or a relative path file.
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Cool, so if you wanna dig into this further,
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there's the documentation path right there.
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Let's go and switch over to our application now
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and hide our browser back away.
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So we know that these are defined within our package.json,
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so let's scroll down and take a look at our package.json.
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You wanna scroll down just a little bit
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until you see this imports object right here,
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where we see a number of different
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subpath namespaces defined.
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We have one for our controllers, exceptions, models,
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mails, services, listeners, et cetera.
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With every fresh AdonisJS 6 project,
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Adonis has set these up for us automatically
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so that we don't need to go in and manually define them
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whenever we get to the point where we're working with them.
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They know that these are most likely
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going to be directories that we need to work with
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at some point through our applications development.
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So they've gone ahead and defined them for us here
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so that we can make easy use of them.
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However, there may come a time
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where you need to define your own
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because you're using something to your own taste
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or specifications.
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For example, a lot of people like to use DTOs or ViewModels,
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so you could add those into your project
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and then define the subpath alias
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for those various import paths.
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So we're gonna end up getting rid of the work
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that we do within this lesson here.
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I just want to highlight how you can add
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your own subpath imports in should you need to.
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So let's roll with the ViewModel example.
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So within our app directory, let's create a new file
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and let's create a new directory called view_models.
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And within here, we'll create a new file called movie.ts.
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So now we have both a movie model and a movie view model.
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Now, as the name suggests, the movie model
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defines what a movie is per our database.
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The movie view model then defines
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what a movie is to our views.
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So they're just models with two different purposes
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within this particular example.
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So that we don't spend too much time on this example,
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I'm just going to go ahead and export default class,
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movie VM, and I'm just going to extend our movie model
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just like so.
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If we wanted to make it obvious
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which one we were working with,
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we can go ahead and add an additional property on here.
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So public type equals ViewModel, something like that.
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So now this type property only exists on our ViewModel
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and not on our movie model.
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Okay, next, let's go ahead and jump
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into our movies controller and let's make use of it.
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So instead of using our movie
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to query all of our different movies,
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let's go ahead and switch this over to our movie model.
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So we'll go ahead and just use automatic imports here
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and we'll scroll down to our movie VM right here
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and go and give that an import.
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And the first thing you'll notice
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is that this is a relative path import that it has added.
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And that's because we haven't defined
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a sub path import quite yet for our ViewModels directory.
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So it's telling Node.js to look for this file at ./
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which goes back a directory from where we're at.
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So out of controllers and into app, into ViewModels
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and then into movie.js.
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Now the file extension is here as we described earlier
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because we're working with ECMAScript modules
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and the file extension is needed
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for relative imports for those.
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Now you might notice that this is a .js file
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despite the actual file being movie.ts.
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The reason behind that to my understanding
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is that it was a TypeScript decision
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because at the end of the day TypeScript
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compiles down to JavaScript
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and they didn't want to mix and match the file extensions.
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So that's why that is there to my understanding.
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Okay, so before we switch this over to a sub path import,
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let's go and give it a test
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just to make sure everything's still working A-okay.
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So let's dive back into our browser
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and give our homepage a refresh where we swap this in.
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Okay, good, everything's still working.
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We can hide that back away.
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And now we know that we need to define our sub path import
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within our package.json file.
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So let's dive down into there.
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And just after our models,
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let's go ahead and add in our view models.
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So we'll do a string hash view_models/*
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designating that the view models namespace
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will work for any file within here, colon.
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And now we can add in the value for this,
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which should be a relative path to the files.
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So add in a string ./,
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which is the start of a relative path
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coming out of our applications root.
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So if we scroll up a little bit,
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we'll want to go into app view_models/*.js
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to support any file within our view models.
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So we'll go app view_models/*.js.
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Give this a save.
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And now we can jump back into our movies controller
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and let's switch this relative import
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for our sub path import.
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So we can get rid of the ./ and replace it with a hash.
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And now we can just get rid of the file extension
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and voila, everything is happy so far.
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However, there is one more step that we need to take.
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Sub path imports are one area where JavaScript
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and TypeScript don't communicate too well with one another
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and TypeScript isn't actually going to read these imports
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from our package.json file.
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So we need to inform TypeScript about them separately.
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So we'll have kind of a one-to-one mapping
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in two different places
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within both of our nodejs package.json configurations
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and our tsconfig.json file.
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So if we scroll down to our tsconfig.json file,
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we will see a paths object like so
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with all of the same mappings that we have
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within our package.json file,
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except they're here now for TypeScript.
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So in order to make use of the sub path alias,
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we'll also want to define our view model sub path alias
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within our TypeScript paths as well.
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Everything here will look pretty much the exact same.
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The only difference is the value will be an array
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rather than just a string.
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And now we should be able to jump back into our browser,
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give our homepage a refresh and everything still works A-OK
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despite us now importing using sub path aliases
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for our movie view model.
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Okay, so within this series,
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we're not actually going to be working with view models.
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So we'll go ahead and get rid of what we've just done.
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But before we do,
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let's go ahead and summarize
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what exactly we covered in this lesson.
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So first, hashes within your imports
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designate sub path imports,
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and you can define your own,
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but you need to do so within both the tsconfig.json file
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and the package.json file.
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Within the tsconfig.json, it will be within paths.
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I'm gonna go ahead and get rid of our view model import here.
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And this paths property is specifically
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within the compiler options.
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Within our package.json file,
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it's gonna be within imports.
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So we'll go ahead and get rid of the view models there
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as well.
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If we scroll up,
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imports is just a baseline property
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within our package.json file.
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The package.json import is needed for node.js,
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whereas the tsconfig.json import is needed for TypeScript.
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You can do relative path imports.
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So if we go back a couple of steps here,
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this works A-okay,
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but you will need to add in .js
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because we're working with ECMAScript modules.
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And you'll need to use .js
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regardless if it's a TypeScript file.
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So we'll give that a save.
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And now we're ready to go ahead
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and just delete out of our view model.
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So we'll go into here,
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right click it and delete.
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And now it's gone.
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And then we'll need to remove the import
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and switch this back to just movie.all.
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Give it a save.
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Let's jump back into our browser one more time just to make sure everything's working A-OK.
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And there we go.
Join The Discussion! (4 Comments)
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news-zanndo
Not present by default in tsconfig.json
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tomgobich
Hi news-zanndo! Yes, as of TypeScript 5.4, TypeScript will now automatically use the subpath imports defined within your
package.json, meaning we no longer need to redundantly re-define them inside thetsconfig.json.Apologies, I thought I had updated the body text for this lesson noting this, but evidently, I did not. Will do that now.
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noctisy
Thank you for the explanation!
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tomgobich
Anytime, noctisy!!
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