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Let's come back to interfaces for objects.

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You can also define optional properties in interfaces and also in classes as I will show you.

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For Dad you add your property name let's say output name here can be whatever you want of course.

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And that should be a string but I don't want to force every class based on name to have that.

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It should be optional whether you want to have that or not.

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You can specify an optional property by adding a question mark after the property name.

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This tells typescript that this property might exist in classes that implement this interface but it

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doesn't have to.

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And therefore we get no error here in person either though I don't have the output Name property because

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it is optional.

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Now of course I can add output name here and initialize this with some value or use it like any other

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property.

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But I don't have to know on a class you can also have an optional property let's say name here should

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be optional because maybe we don't get a value here for n we can add a question mark here as well in

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our class we now adjust all to have to make it optional here in named otherwise we violate against our

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interface which for assistance to be a string.

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Now I'm saying this can be optional.

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So here it's not optional and here when I set this equal to N I only want to do this if n is truthfully

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if it is set.

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So only if it's not an empty string for example otherwise name will not be set.

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And Dad is okay because I turned out to be an optional property both here in the interface but also

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in my class.

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So now a year when we construct a new object we could do this without passing in a name to allow that

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we have to go to the constructor and provide a default value here or also add a question mark here does

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this also allowed.

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You can add optional parameters either by providing a default full back value or by adding a question

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mark in which case the default value will be undefined.

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And now we can call this constructor without a value because we have that optional parameter and because

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we have the optional property that is OK we don't need to initialize it and hence thereafter if we create

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well this name of course will yield on the fine.

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So probably we should check here as well if we got a name and if we do we can't lock this else we can

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so lock high without any reference to the name because we don't have one if we save that everything

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compiles and we see just high here because it didn't provide a name so that would be optional properties

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both in a class and in an interface and also in my constructor list here.

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And now just to make it really clear again these free things are only loosely related.

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You can have an optional property in an interface and then implement it as a non optional property in

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the class.

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You then just have to make sure that your logic is such that this is always initialized otherwise you

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get an error as you just saw or you have an optional property in an interface and an optional property

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in your class then you don't have to assign a value in all cases here.

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And in addition in all the totally unrelated here you can have optional parameters in functions and

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therefore also in methods including the constructor method optional parameters are defined either with

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the question mark where the default value if not set is therefore undefined or simply by assigning a

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default value like this.

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Then as you learned this is also optional and the default value will be assumed if you don't pass in

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a more specific value.

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So this gives you more flexibility in how you structure your classes.

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And when we talk about interfaces how you structure your contracts classes might need to adhere to.