[Syntax Error?] What is "!"?

[vadya-coder]

Apparently, I do not know js. What is "!"?

react-redux/src/hooks/useReduxContext.ts

Line 22 in 56dbf28

return contextValue!

[EskiMojo14]

it's typescript specific, it's a non-nullish assertion. Basically it's the equivalent to return contextValue as NonNullable<typeof contextValue>