An example which shows how to write a callback function and a callback-accepting function..

Callback Function

// Create a function that accepts another function as an argument
const callbackAcceptingFunction = (fn) => {
  // Calls the function with any required arguments
  return fn(1, 2, 3)
}

// Callback gets arguments from the above call
const callback = (arg1, arg2, arg3) => {
  return arg1 + arg2 + arg3
}

// Passing a callback into a callback accepting function
const result = callbackAcceptingFunction(callback)
console.log(result) // 6