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The last interesting type I want to show in this module is to never type.

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Now we saw a function that returned white so that never returns anything.

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Never is another type.

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Functions can return.

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And that might sound strange.

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Let's have a look at how it works.

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Let's say we have a function generate error or here I expect to get a message which is a string and

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maybe some error code which might be a number.

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Now inside of this function let's say we throw an error.

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So this should essentially be a utility function that generates error objects and throws them.

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So here we might throw an object which we can do in JavaScript we can throw any object or any value

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as an error and that should have a message.

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Property in which I stored the value of my message argument here and I want to have an error code property

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let's say we're a store to code argument in.

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So now it is would be a valid function and we can call this with an error occurred for example and a

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code of 500.

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If we do that and we compiled is file here we see that once this reloads we get our error.

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Well as an error here and this might sound pretty abstract but actually it isn't having utility functions

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like this would be pretty standard in bigger applications where you don't manually want to throw an

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error in ten different places of your app but where you want to reach out to one convenient function

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that builds the error object for you and maybe also froze it immediately so that you can call this function

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with different inputs but you always have an error being thrown.

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Now the interesting thing about this function is it does not just return wide.

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I actually can specify that it returns wide because of course returns nothing but actually does not

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just return nothing.

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If we're totally honest this function returns never.

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This function never produces a return value.

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If I would try to restore the return value here and a console log result and I then compile my code

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and this executes we see there is no undefined being locked here because since an error is thrown this

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essentially crashes our script.

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You could say it cancels our script and this will always be the case for this function.

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Of course we can wrap it and try catch so that we can still continue in the script.

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But this function essentially never produces a value.

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This function always crashes the script or this part of the script.

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If you're using try catch and therefore never returns anything and hence the return type of this function

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actually is not just wide but also never.

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Now the interesting thing is if you hover over it without assigning never you see the inferred type

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as white all because never is a newer type.

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It's been around for some time now but it wasn't built into the first versions of TypeScript and therefore

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why it is typically assumed and it's not horrible to leave it at that but you can be very clear and

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explicitly set.

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Never asked the return type to make it really clear that this never returns anything.

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So from a code quality perspective this might be clearer regarding your intentions and make it really

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clear to average developers reading your code that this function is intended to never return anything

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and to essentially crash or break your script or that part of the script and no function that would

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never return by the way would be a function with an infinite loop.

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So if we have while true in there that creates an infinite loop and that therefore all would be a function

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that never returns the error function here or the function that generates and throws an error probably

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is the more common use case though so never.

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Also an interesting type which you can use on functions for cases like this one here.