In simple terms, what's the difference between a thunk and a Higher Order Function?

Question

I understand that both are functions that return functions.

My experience so far with thunks have been using them to return functions as opposed to just action objects so that I can work with async requests in Redux.

A closure is an implementation of a High Order Function (HOF) in order to create a new scope for private variables...right? Other examples of HOFs include map, reduce and filter.

Is there any thing else that explicitly defines a difference between the two?

Thanks.

Answer 1

I understand that both are functions that return functions

Your understanding is slightly incorrect

• Thunks can return a value of any type – not just a Function type
• Higher-order functions can return a value of any type – not just a Function type

My experience so far with thunks have been using them to return functions as opposed to just action objects so that I can work with async requests in Redux.

Thunks (and higher-order functions, for that matter) are not intrinsically related to any particular library (React, Redux) or any particular control flow (sync, async). A thunk is just a nullary function – they have a variety of common uses cases, but most commonly are used to delay the evaluation of a specific computation.

A closure is an implementation of a High Order Function (HOF) in order to create a new scope for private variables...right? Other examples of HOFs include map, reduce and filter.

A closure is not necessarily an implementation of a higher-order function. The function keyword (and => arrow function syntax) does create a closure tho which does have a new (lexical) scope, yes.

Is there any thing else that explicitly defines a difference between the two?

Yes. How they are the same:

• they are both functions
• they can both return values of any type

How they are different:

• thunks are nullary functions (they accept no arguments)
• higher-order functions accept a function as an argument and/or return a function

Perhaps the most critical distinction:

• A thunk can only be considered a higher-order function if it returns a function.