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Now loosely related to optional Cheney we got another nice feature in typescript which helps us deal

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with knowledge data and that feature is called knowledge coalescing.

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Now imagine you have some data some input where you don't know with certainty whether it's now or on

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the find or whether it's actually a valid piece of data.

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For example user input could be now let's say now again here we hard code doesn't to typescript hence

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typescript knows that this is now.

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But if you're fetching this through some DOM API where you don't know it with certainty or if you're

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getting this from a back end then you might not know in advance and typescript might not know where

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it is is null or not if you didn't want to store this in some other constant or variable like stored

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data.

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You might want to make sure that if it is now you store a fallback value.

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Now you can do so with the logical or operator where you store a default where you get that second value

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of the first one is undefined or.

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Now if it's false C to be precise.

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The problem with this approach is if this is actually not now or undefined but let's say an empty string

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it is treated as a false value and data for debt default fallback value will kick in.

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So if I set a console lock stored data here you will see that this prints default now maybe it is what

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you want and in that case this is a perfectly fine solution but if you want to keep that user input

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or whatever data you're working with unless it really is now or undefined then you need another approach.

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Because here we would treat this as false and use the fallback.

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But maybe you want to keep an empty input just null or undefined should be handled differently for that

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type could also has an operator.

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The double question Mark.

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Operator this is called The Knowledge coalescing operator and it means if this is null or undefined

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and really just that not an empty string not zero really just now or undefined then we'll use the fallback

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if it's not Nala on the find.

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We'll use that value.

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So in this scenario here this compiles and you see we stored the empty string.

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Hence I'm not printing anything here.

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This is the empty string.

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If is on the other hand let's say is undefined here in safeties.

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You say now it says default because thanks to this double question Mark.

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Operator we fall back to this.

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Well back and therefore here we got a number very useful feature which can help you deal with knowledge

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or undefined values with grace.