i need help calling a function-CodePudding

i have a task to do (based on nothing we have learnt.. this is part of the challange, but i cannot do it nor know what i am supposed to search i have tried everything.

this is the task:

/**
 * Create a function that accepts two numbers,
 * and calls the callback with the sum of those numbers
 * @param {number} x
 * @param {number} y
 * @param {Function} callback
 */
function sumAsync(x, y, callback) {
  
}

export default sumAsync;

can someone point me to the right direction? are they asking a function inside a function? if so, where can i read about it and know how to do so?

CodePudding user response：

This should work:

/**
 * Create a function that accepts two numbers,
 * and calls the callback with the sum of those numbers
 * @param {number} x
 * @param {number} y
 * @param {Function} callback
 */
function sumAsync(x, y, callback) {
  callback(x y);
}

EDIT: Explanation: This will call the function that you set as callback parameter, you can use it as: sumAsync(2, 3, console.log); so your function will call the callback function (console.log here) with the parameter x y, so console.log(x y); and print 5.

CodePudding user response：

can someone point me to the right direction? are they asking a function inside a function? if so, where can i read about it and know how to do so?

Javascript allows you to pass functions as variables. What that means is you can create a function and then pass it to another function, which then calls it (this is a 'callback').

function updateString(someString) {
  return someString   ' - got updated';
}

function modifyString(someString) {
  return someString   ' - got modified';
}

function complexStringPlusCallback(myString, callbackFunction) {
  myString = myString.split().reverse().join();
  myString = callbackFunction(myString);
  myString = myString.toUpperCase();
  return myString;
}

// notice that we pass in `updateString` rather than `updateString()`
console.log(complexStringPlusCallback('abc', updateString));
console.log(complexStringPlusCallback('123def', modifyString));

In this scenario, passing a callback function means we can change the middle part of complexStringPlusCallback without needing to make two functions (or three if we added a third possible callback).

There are a lot of reasons callbacks are used. They let you pass functions to modules or objects which will call them when an event occurs, for example - so you can have a function be automatically called whenever a user clicks on a button.

If you want further reading on the topic, a function that takes a function as a parameter is called a 'higher-order function'.

I'm going to assume getting the sum of the two numbers is trivial and won't address that part.