Recall that our overarching goal in this lesson is to give you the tools you need to add asynchronous functionality to your Redux apps. One of the most flexible and popular ways to add asynchronous functionality to Redux involves using thunks. A thunk is a higher-order function that wraps the computation we want to perform later. For example, this add() function returns a thunk that will perform x+y when called.

const add = (x,y) => {
  return () => {
    return x + y; 
  } 
}

Thunks are helpful because they allow us to bundle up bits of computation we want to delay into packages that can be passed around in code. Consider these two function calls, which rely on the add() function above:

const delayedAddition = add(2,2)
delayedAddition() // => 4

Note that calling add() does not cause the addition to happen – it merely returns a function that will perform the addition when called. To perform the addition, we must call delayedAddition().