Generics. By default, the type checker considers null and undefined assignable to anything. Don’t ever have a generic type which doesn’t use its type parameter. Contextual typing with a return type of void does not force functions to not return something. We make it clear which is the return type by using an arrow (=>) between the parameters and the return type. Nullable types. S and T are object types and, for each member M in T, one of the following is true: M is a call, construct or index signature and S contains a call, construct or index signature N where. No matter which expression is evaluated, void always returns undefined. In Typescript (using in an Angular project) for a method that returns nothing (void), which of the below is best practice? The second part is the return type. Return type void. And it works fine for return values of functions. We mentioned these briefly in the Basic Types section. TypeScript has two special types, null and undefined, that have the values null and undefined respectively. Important to note that void and any types overlap a bit, which may be weird at first. And in both worlds void works a little bit different than most people are used to. Did you forget to include ‘void’ in your type argument to ‘Promise’? Have your JS expressiveness and type it too. See more details in TypeScript FAQ page. The void type is pretty much the opposite of the any type. Instead of Object, use the non-primitive object type (added in TypeScript 2.2). onSelect(someNumber: number) { } I've seen it both ways in different examples and wasn't sure if it is better to add the return type as void … Then, I figured out that TypeScript infers the type of the callback's parameter e to be an intersection(&) of MyMouseEvent and MyKeyboardEvent: e: MyEventObjects[K] >>>> e: MyMouseEvent & MyKeyboardEvent the result type of M is Void, or the result type of N is assignable to that of M. In this case, we're testing if => string is assignable to => void. onSelect(someNumber: number): void { } OR. However when void is a type of an argument it's not that clear what value can be used for it. The void return type for functions can produce some unusual, but expected behavior. Is there a way to specify a parameter for an argument of the void type? Allow me to quickly answer to "normal" use case of "How to define function overload types with TypeScript" with an example: I want a function that accepts a callback or returns a promise if none is provided: void in JavaScript # void in JavaScript is an operator which evaluates the expression next to it. Require explicit return types on functions and class methods (explicit-function-return-type) Explicit types for function return values makes it clear to any calling code what type is returned. any. It is possible to specify void as a type parameter for generic function in TypeScript. 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