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1How to type annotate functions?
2How to set the return type of a function as promise?
3How to make a parameter of a function optional in TS?
4How to receive a function as a parameter?
5How to set types for parameters of multiple, predefined types
6How can we extract return type of a function in typescript? What are the use cases?
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How to make a parameter of a function optional in TS?

In TypeScript, every parameter is assumed to be required by the function. You can add a ? at the end of a parameter name to set it as optional.

Optional parameters must come after all non-optional parameters: