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Now I mentioned that interfaces are used to define the structure of an object.

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Now interfaces can all be used to define the structure of a function.

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So basically as a replacement for the function types you already learn about just as a quick refresher

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we can define the type of a function.

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For example with a custom type with the type keyword at f n for add function which then could hold a

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function definition like this.

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It should return a number and it should take two arguments where each argument also is of type number.

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Now we could create a new function add here which is of type at f n and when we don't initialize it

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but assign our function later then of course we have to make sure that this function takes two arguments

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which are of type number and that in there we all return a number.

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This is something we can do.

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This is what you already learned.

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Now you can also use an interface as an alternative to this custom type interfaces are there to define

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the structure of an object as it taught you.

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But in the end functions are just objects and therefore this is a little exception.

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You can create function types with interfaces for Dad you create an interface name it add if and to

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still keep that name here and now in there.

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You defined a bit of function by just adding parentheses with your arguments a number B number for example

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and then a colon not an arrow but a colon here with the return type.

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So in the end like you would define a method as we're doing it here with Grete with the exception that

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we're now not adding a method name.

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So we have an anonymous function if you want to call it like this in the at f an interface and typescript

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understands this special syntax off this anonymous function in your interface and understands that you

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want to use this interface as a function type and this is how your function should look like.

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So now we can use ADF and here and indeed if I would try to accept a string here we would get an error

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because this is not a sizeable we need to have a number instead of a string.

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So it's simply an alternative to this custom type of course here.

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I would argue using a custom type is probably a bit more common.

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It's all a bit shorter but it's a nice alternative syntax to be aware of especially if you encountered

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as in some project and your other wise lost.

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What this means.

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This strange anonymous method.

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Well it's in the end just a custom function type.