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So now we got union types here.

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Let's build upon that idea of union types and also introduce literal types literal types are types where

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you don't just say that a certain variable or parameters should hold let's say a number or a string

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but where you are very clear about the exact value it should hold.

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We saw that early already here in basics concept number two for example.

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Therefore hover over that you see the type which was inferred is not no it's two doors eight and types

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did in third this concrete number as a type here because it's a constant.

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It will never change in the effort hive knows the value I assign here is the exact type I have.

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So of course this is a number you could say to dot eight is derived from the number type but it's a

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specific number.

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And this does not just exist for numbers but all four strings ends on and especially for strings it

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can be very useful let's say here in our combined function we expect numbers or strings and we combine

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them differently based on what we get but we also want to allow the caller off the function to define

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how the results should be returned.

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So that we can basically force a conversion from number to string or the other way around.

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We could do this with a third parameter and we could name that let's say it result type or result conversion

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or however you want to name it.

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And I want to describe this with a string is all set as to type string.

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No my idea is that I can call combine year with two numbers.

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And for example pass in a string of as number and it's totally up to you which identifier you use here.

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Down there we might have as text but then we might have another combination here

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combined string ages where I pass in two strings but I still want to put this as number and this would

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be a case where the third parameter can be helpful to force a conversion because if I pass in two strings

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here normally we would make it into this ls branch and concatenated and I might want to return this

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as a number instead so that I can all the console log combined string age is here.

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So now we just have to take these identifiers into account in our function by including a result conversion

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in our if checks.

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Now the question is what exactly do we want to do.

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Do we want to make sure dead we can force these two strings to be added as numbers or do we want to

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force the result no matter if it was a mathematical calculation or a string concatenation to be converted

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to a text or a number if we want to force a conversion we could ATF check here and check if it's salt

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conversion is equal to as no and if that's the case I want to return resolved with a plus in front of

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it which converts it to a number.

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The alternative would be parse float for example but here I'll just go for the plus since this is a

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bit shorter and else I want to return result to string to forests and output as a string.

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So now we do the calculation based on the real type we get but then we convert the result that's one

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way of doing that and if we save that and we then compile this file we see this is the result I get

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and we get Dad output for example for our string combination here because as I said the combination

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itself the calculation so to say is performed based on the type we feed in which here is a string.

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So we concatenate it and then we just convert to result.

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The alternative logic would be to check the type here and do a different operation based on the return

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type or specifying here.

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So we could comment this out and instead here say if the type of input 1 is number and type of input

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2 is number or if result conversion is equal to AS number then I want to combine values like this and

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now to a white as error here I forced the conversion to numbers by adding a plus in front of each input

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so that each input is converted to a number and is guaranteed to be a number before I combined them.

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Side note if you would pass in strings that can't be converted to a number so something like Max for

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example.

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Then you'll get an A n not a number as a result.

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Well in the Dallas case so that we don't have as number or that we simply don't have no inputs.

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Then we make it into this block here and now with that if I return result again here and we didn't safeties

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and recompile we'll see a different output on our page.

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Now we get 56 in these two lines here because now we're not converting the result.

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So we're not converting that concatenated string for this line but instead we're doing the conversion

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before we combine the two values.

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So that's up to you which logic you want to implement.

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I actually want to have a closer look at literal types concept which I described at the beginning of

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this lecture I'm passing in as number and asked text and the downside of this is that right now we as

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a developer have to memorize these values we have to make sure that we don't miss type here.

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Now we could use that income to improve that but if we only have two values here as text or as number

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then maybe alls and such a literal type could be an option we could say this shouldn't be any string.

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It should be as number or as text.

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So we use a union type combined with literal types literal types are the types which are based on your

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core types.

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String number and so on but you don't have a specific word in off that type.

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So here we allow us specifically these two strings not any string just these two strings.

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So we want a string for resolved conversion but it has to be one of these two values.

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Any average string value will not be allowed.

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So that's the idea behind a literal type.

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And often you will use this in the context of a union type because you don't just want to allow one

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exact value you could hardcoded into your code if that would be the case but you want to have two or

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more possible values.

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In this case we get two possible values.

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So now we are guaranteed to get result conversion which is either as number or asked text for example

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here if I now try to compare this to as number because I have a typo here typescript is able to tell

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me here in the ITC and of course all if we save it and compiled here in the terminal because it knows

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that as number without a r at the end will never be a valid value for a result conversion because I

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set this union type with these literal types.

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So now we again gain some extra type safety and ensure that we can't use this incorrectly the same of

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course for passing in a value if we have a typo here we get an error only if we use ever as number or

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s text we're allowed to compile this as you see if I now compiled is does works and we get the same

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output as before year.

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So these are literal types especially useful when used in conjunction with union types.