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In the last video we spoke about two big issues in getting typescript mongers to work together.

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We wrote out this model and everything looks good right now.

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But as we saw as soon as we start to try to create a user we can start to run into some issues because

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typescript is not checking the type of arguments we are passing to that constructor.

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So this video we're going to figure out how we can solve issue number one.

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How can we make sure that typescript is going to check the type of arguments we are passing into this

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user constructor to solve this.

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I'm going to go back over to my editor.

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I can go to the top of the file right after the import statement.

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I'm going to write out a new interface right here.

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I'm going to put a comment on this interface just we understand what it is doing.

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As we go into the future it's going to write out in and comment that says an interface that describes

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the properties that are required to create a new user so in our case to create a new user you must provide

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an email that's a string and a password that is a string.

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That's what we want to have.

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So I'm gonna write out an interface that describes this object right here.

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I'm going to call this interface user adders adders is short for attributes.

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So these are the attributes that are required to create a new user inside this interface.

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I'll write out an email that has a string and a password that is a string.

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We are now going to use this interface to make sure that each time we try to create a new user we are

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passing in the correct set of attributes.

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To do so we're going to use a little trick and this trick is going to be something that we're going

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to keep in mind for all the rest of this application.

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Anytime we tried to create a new user.

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Let me show you what we're gonna do now at the very bottom.

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Right after we create our new user or the actual user user model I'm going to define a new function

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called Build user anytime that we want to create a new user.

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We are going to call this function instead of calling new user.

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So this is something this is a little trick.

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This is the thing that you need to keep in mind all the Mongoose documentation that you're ever going

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to look at or blog posts and so on are going to say oh you had to create a new document you called New

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than the name of your model and you pass on the attributes we are not going to follow that because we

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can not really do effective type checking with typescript if we follow this pattern instead anytime

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that we want to create a new user document.

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We are going to call this build user function.

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So that is the very important thing that you keep in mind going forward as the argument to this function.

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I'm going to receive an argument called adders and we're going to put in a type here of user adders

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and then inside all we're going to do is turn right around and return a new user that gets fed that

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set of actors.

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So we're really doing here is putting in this extra little step just to get typescript involved in this

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process of creating a user because we are never going to write out new user directly inside of our code.

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Instead we're going to call build user typescript is going to be aware of the set of arguments that

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must be provided to this function typescript knows we have to pass in an object that has an email that's

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a string and a password that's a string.

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So now so long as we only ever create a user by using this function type scripts going to have our back

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and make sure that we are providing the correct set of arguments.

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Now we can try to test this out by writing some similar code to what I showed you just a little bit

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ago when we were trying to call new user directly with a set of arguments that didn't make any sense

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if I called build a user and pass in an object I'm going to throw in an email and a password if I now

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start to add in any additional arguments like let's say something like that right there typescript going

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to jump in and say nope don't do that.

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Awesome.

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That is what we want.

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We want typescript to jump in and tell us that we are making a mistake in creating a user if I ever

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make a typo in a property name.

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So for example if I accidentally type out pad once again typescript has our back and if we ever tried

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to assign a property or provide a property that is the incorrect type type skips going to have our back

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as well if I put in a type of number right here instead of a string as says hey sorry but this really

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needs to be a string okay.

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So that's it.

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That is how we are going to solve issue number one.

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We're going to make sure that we do not call new user directly at any point in time even though that

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is what the official documentation says.

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Instead we are going to use this build user function because this is how we can get typescript involved

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in the process of making sure we are passing in the correct set of attributes so we probably want to

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make sure that we export this function like so.

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All right.

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So now having said that having it repeated to you like four times this is how we going to create a user.

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I do want to throw out a little kind of uncertainty here so right now we've created this new function

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and now any time we want to create a user or kind of work with users in any way.

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We now have to import two different things from this file that is not super convenient.

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So even though this approach works right here I'm wondering is there some way that we can improve it.

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Is there some way that we can still make building a new user or creating a new user at least somewhat

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similar to what we were doing before so that we don't have to have this really high mental burden as

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engineers and have to memorize.

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Oh yeah.

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I always need to import this buildings or function any what time I want to create a new user.

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So I'm thinking although this definitely works maybe we can take a very similar approach but express

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it in a slightly different fashion just to make it a little bit more convenient for us so that minds.

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Let's take another pause right here.

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We're going to figure out how to rewrite this slightly to make it just a little bit more convenient

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to use.