Welcome to Fruit Picker on Exercism's JavaScript Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Callback functions are functions passed as arguments. This programming pattern creates a sequence of function calls in both synchronous and asynchronous programming. Writing a callback function is no different from writing a function; however, the callback function must match the signature defined by the calling function.

const squareLength = 5;

// Caller function takes a callback function
function applyToSquare(callback) {
  return callback(squareLength);
}

// Callback must expect the possible argument from the calling function
function areaOfSquare(number) {
  return number * number;
}

applyToSquare(areaOfSquare); // => 25

You may also write callbacks as a function expression:

applyToSquare(function squarePerimeter(side) {
  return side * 4;
});

You are creating a new online portal for your patrons to order their fruit fresh from the grocer. The grocer has an API that you can use to see if they have the inventory desired by your customers. You need to create a small library of functions for interacting with the grocer's API.

Write a callback function called onSuccess to be called when the order is successful. It should invoke the imported notify function passing a success message to it.

onSuccess();
// => `notify` called with `{ message: 'SUCCESS' }`

Write a callback function called onError to be called when the order encounters an error. It should invoke the imported notify function passing an error message to it.

onError();
// => `notify` called with `{ message: 'ERROR' }`

The grocer's API provides a function to order from their inventory called order. It receives three arguments: a query, a callback function to be invoked when the order is successful, and a callback function to be invoked when the order encounters an error. You decide to wrap the api function call in a newly defined function orderFromGrocer to insulate your codebase from external changes. Your function should forward the arguments (which match the provided api function) to the api function.

The query takes the form of an object:

const query = {
  variety: string,
  quantity: number,
};

orderFromGrocer(
  { variety: 'pear', quantity: 12 },
  exampleSuccessCallback,
  exampleErrorCallback,
);
// => `order` was called with the query and the callbacks

You find that you are calling this function from many different places with the same functions. Seeing an opportunity to refactor your code, you want to create a function where you can supply the variety and quantity to order as arguments.

postOrder('peach', 100);
// => order submitted for 100 peaches

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