Eloquent JavaScript - Chapter 4 - Data Structures Objects and Arrays (Notes)

*Exercises

The sum of a range

function range(start, end, step) {
  // If no optional step, set step to 1.
  if (step == null) step = 1;

  // Initialize the array that will eventually be returned.
  var array = [];

  // If the range is increasing, continue pushing i to the    
  // array and incrementing i by step until i is greater than 
  // end, then stop.
  if (step > 0) {
    for (var i = start; i <= end; i += step)
      array.push(i);
  // If the range is decreasing, continue pushing i to the 
  // array until i is less than end, then stop.
  // Remember i will get smaller because step is negative.
  } else {
    for (var i = start; i >= end; i += step)
      array.push(i);
  }
  // Return the result
  return array;
}

function sum(array) {
  // Set total to start at 0.
  var total = 0;
  // Go through each item in the array and add it to result.
  for (var i = 0; i < array.length; i++)
    total += array[i];
  // Return result.
  return total;
}

console.log(sum(range(1, 10)));
// → 55
console.log(range(5, 2, -1));
// → [5, 4, 3, 2]

×Reversing an array

/*function reverseArrayInPlace(array) {  for (var i = 0; i < Math.floor(array.length / 2); i++) {    var old = array[i];    array[i] = array[array.length - 1 - i];    array[array.length - 1 - i] = old;  }  return array;}*/
function reverseArrayInPlace(array) {
  for (var i = 0; i < Math.floor(array.length / 2); i++) {
    var old = array[i];
    array[i] = array[array.length - 1 - i];
    array[array.length - 1 - i] = old;
  }
  return array;
}
*/

function reverseArrayInPlace(array) {
  var b = array.length;
  for (var i = 0; i < --b; i++) {
    var swap = array[i];
    array[i] = array[b];
    array[b] = swap;
  }
  return array;
}

function reverseArray(array) {
    var output = [];
    
    for (i = array.length - 1; i >= 0 ; i--)
    {
        output.push(array[i]);
    }
    
    return output;
}

console.log(reverseArray(["A", "B", "C"]));
// → ["C", "B", "A"];
var arrayValue = [1, 2, 3, 4, 5];
reverseArrayInPlace(arrayValue);
console.log(arrayValue);
// → [5, 4, 3, 2, 1]