Argument type restriction in TS function declaration [duplicate]

Question

I came across some function declaration like below.


type DataType = TypeA | TypeB | TypeC;

function Func(data: DataType): data is TypeA {
...
}

I don't understand the is part of the declaration. How it affects the return type of the function?

Also relevant: Interface type check with Typescript How to get a variable type in Typescript? Typescript: Check “typeof” against custom type — VLAZ
– VLAZ, Commented Jun 21, 2020 at 23:04

itsanewabstract · Accepted Answer · 2020-06-21 23:00:12Z

0

This Stackoverflow post might help you understand the is keyword a little better.

answered Jun 21, 2020 at 23:00

itsanewabstract

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