Encountering an issue: a function is required to return a value if its declared type is not 'undefined', 'void', or 'any'

Question

I have a specific function type that is capable of returning either void or Promise<void:

export type CommandHandler = (values: CommandValues) => void | Promise<void>;

Currently, I am attempting to utilize this function type in a void function:

export const handler = (values: CommandValues): CommandHandler => {
  console.log(`hello ${values.name}`);
};

However, an error message is being displayed regarding the usage of CommandHandler:

The function must return a value as it's declared type is neither 'undefined', 'void', nor 'any'.

This situation has left me puzzled. I have clearly specified in the type that the function can be of type void. So, why is there an issue?

Based on my understanding, there should not be any errors due to how I've defined the function.

Answer 1

Answer №1

: CommandHandler within your code indicates the expected return type. TypeScript requires the function to return a function based on this typing.

export const handler = (values: CommandValues): CommandHandler => {
  console.log(`hello ${values.name}`);
};

To provide a type constraint to the entire function, you may want to use the following approach:

export const handler: CommandHandler = (values: CommandValues) => {
  console.log(`hello ${values.name}`);
};

Answer 2

: CommandHandler within your code indicates the expected return type. TypeScript requires the function to return a function based on this typing.

export const handler = (values: CommandValues): CommandHandler => {
  console.log(`hello ${values.name}`);
};

To provide a type constraint to the entire function, you may want to use the following approach:

export const handler: CommandHandler = (values: CommandValues) => {
  console.log(`hello ${values.name}`);
};