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Now if we come back to this interface here the question is why do we need this wouldn't we have the

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exact same thing if we would at a custom type here and there.

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The difference is just that we have to have a equals sign and then we're saying the person type is an

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object which looks like this.

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And indeed if we saved added compiles without errors so we could replace our interface with such a type.

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And it works as before.

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So why do we have an interface then.

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Well an interface and a custom type are not exactly the same.

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Whilst often you can use them interchangeably and you can use the interface instead of a custom type

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or the other way around.

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There also are some differences.

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Well one major difference is that interfaces can only be used to describe the structure of an object.

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You can use type for that as well but instead of a custom type you can also store other things like

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union types and so on what we did earlier in the course that sounds like type is therefore more flexible.

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But the other side of the coin is that interface is clearer when you define something as an interface.

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It's super clear that you want to define the structure of an object with that.

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And indeed when it comes to defining object types you more often see interfaces out there in the wild.

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Then you see custom types.

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Now another thing you can do with interfaces but you would also be able to do with custom types is you

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can implement an interface in a class.

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What do I mean by that.

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The reason why you often work with interfaces is dead.

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Interface can be used as a contract.

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A class can implement and a class then has to adhere to.

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What do you mean with that.

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Let's say our interface is not a person interface with a name in the age but instead we name it.

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Greed double notice might look like a strange name but in the end this just says any object dad should

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be treated as readable has to be object with a name and with a creat method.

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So now we could say this here this user one variable should hold a reasonable object.

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And of course now we get an error because we have more than just name and greet.

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But we could use this interface to share it amongst possibly multiple classes.

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We have to ensure that every class that adheres to this interface has to have a name property and has

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to have a great method.

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So here we could now add a person class the name is available again because I renamed the interface

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and now tell typescript that this class should basically adhere to this interface it should implement

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this interface it should follow that contract set up by this interface.

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We do it by adding the implements keyword offered a class name and then the name of our interface readable.

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And you can implement more than one interface.

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That's a difference compared to inheritance you can inherit only from one class.

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You can implement multiple interfaces by simply separating them with a comma.

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So there we could have another interface if we had one here.

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I only have one though.

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And now the implication of this is that we get an error here because our class incorrectly implements

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the interface.

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It does not have the name property does not have the Greek method.

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So now we have to set this year in our class maybe also add a constructor where we get a value for the

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name and then set it up like this.

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And where we also add our agreed method where we then might have this logic from now there.

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Now in our class we can't have more than that.

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We can't have more fields.

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We can have more methods.

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We can also extend this class.

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We can work with this class as we always can but we're forced to implement this method correctly to

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have this name property because we're implementing this interface and ever interfaces are often used

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to share functionality amongst different classes not regarding their concrete implementation.

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You can't have implementation or values instead of interfaces.

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But regarding the structure regarding the features a class should have.

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It's a bit like working with abstract class to stay up for the difference being that an interface has

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no implementation details at all whereas abstract classes can be a mixture of you have to overwrite

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this parts.

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And I have a concrete implementation parts.

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That's an important difference between interfaces and abstract classes.

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Now with that however we have our Person class here and now here User 1 can be created by using new

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person and feeding in the name for example.

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And now you see it's OK that we have this eight year end user one because we build user one based on

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person person implements treatable and you can add more than treatable ones in a class but you have

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to satisfy the conditions set up by the interface.

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And if for now if we save everything we have a valid code.

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And if we log our user one down there with console log we see that it is a normal object with an age

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and a name in this case.

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But the key takeaway is that it is based on a class which implements the interface and you can then

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all use the interface as a type of course we could have set this to type person.

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But as you see using type Greta here all the works because the person object which we store in the user

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one class in the end is based on the readable interface it implements this.

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So that's another powerful feature you can use an interface as a type on some constant or variable which

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will then actually store and never a class of a number type which in turn is based on the interface

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type because it implements it.

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So that's interfaces in a nutshell.

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Lot of powerful features included.