custom_Callback-1.js

//Example -1 super simple example of custom callback. done() is a callback which I am definining seperately.
done = () => {
  console.log("Done from Callback");
};

printNum = (num, callback) => {
  for (let i = 0; i <= num; i++) {
    console.log(i);
  }
  if (callback && typeof callback === "function") {
    callback();
  }
};

printNum(5, done);

// Example-2, where, I will pass the callback after invoking the function, without defining the callback separately
mySandwitch = (a, b, callback) => {
  console.log(`Started eating my sandwitch.\n\nIt has: ${a} and ${b}`);
  callback();
};

/*mySandwitch('cheese', 'ham', () => {
	console.log('Finished eating my sandwitch');
})*/

// To make the callback optional, we can just do this:
mySandwitchOptional = (a, b, callback) => {
  console.log(`Started eating my sandwitch.\n\nIt has: ${a} and ${b}`);

  if (callback && typeof callback === "function") {
    callback();
  }
};

/* Write a custom callback function which returns the addition of its 2 arguments through a callback. That, the function would take 2 arguments and the third agument would be a callback function. And the final return output of that function would be with callback. - Was asked in Techolution interview */

addTwoArgs = (a, b, callback) => {
  if (callback && typeof callback === "function") {
    return callback();
  }
};

let result = addTwoArgs(2, 5, () => {
  return 2 + 5;
});

console.log(result);