Discussion on: TypeScript Optional Parameters

[ecyrbe]

You don't need to do a runtime typeof JavaScript introspection. Indeed, here c is declared. Use typeof only to check if a variable is declared.

if ( c === undefined )

Just works in your example.

You can use typeof to check for global variables. For example :

window === undefined

will throw an exception on nodejs when it will return false on your browser.
In this case, yes you should use typeof:

typeof window === "undefined"

[Johnny Simpson]

You're right, in fact typeof c == undefined won't work at all since typeof returns a string. I've updated.