Applying of passing functions as parameters in JavaScript

Let's make a function that will take an array as a parameter, and a function as the second parameter. The passed function will need to be applied to each element of the array:

javascriptfunction test(arr, func) {
  // returns the modified array
}

An implementation:

javascriptfunction test(arr, func) {
  // Loop starts:
  for (let i = 0; i < arr.length; i++) {
    arr[i] = func(arr[i]); // apply the function to each element
  }
  
  return arr; // returns modified array
}

Let's apply our function to some array:

javascriptfunction test(arr, func) {
  for (let i = 0; i < arr.length; i++) {
    arr[i] = func(arr[i]);
  }
  
  return arr;
}

// Let's convert an array of numbers into an array of their squares:
let result = test(
  [1, 2, 3],
  function(num) {return num * num;}
);

console.log(result); // shows [1, 4, 9]

Let's make our function call more elegant (it's more common way):

javascriptfunction test(arr, func) {
  for (let i = 0; i < arr.length; i++) {
    arr[i] = func(arr[i]);
  }
  
  return arr;
}

// Let's make the code more elegant:
let result = test([1, 2, 3], function(num) {
  return num * num;
});

console.log(result); // shows [1, 4, 9]