myPop.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>
// MDN Docs notes
// The pop() method removes the last element from an array and returns that element. 

// Parameters
  // array

// Return value
  // The removed element from the array; undefined if the array is empty.

// Pop is intentionally generic; this method can be called or applied to objects resembling arrays. 

// Notes:
// If you call pop() on an empty array, it returns undefined.
// This method changes the length of the array.
// myPop should update the length property of any object, or create {length: 0} if no length property exists.

function myPop(obj) {
  if (typeof obj === 'object' && !Array.isArray(obj)) {
    if (obj.length === undefined) {
      obj.length = 0;
    } else {
      obj.length -= 1;
    }
    return obj.length;
  }
  if (Array.isArray(obj)) {
    if (obj.length === 0) {
      return undefined;
    }
    var poppedIndex = obj.length - 1;
    var returnValue = obj[poppedIndex];
    obj.length = (obj.length - 1);
    return returnValue;
  }
}

tests({
  'It should return undefined if passed an empty array.': function() {
    eq(myPop([]), undefined);
  },
  'It should return the last element of passed in array.': function() {
    eq(myPop([1, 2, 3]), 3);
  },
  'It should modify passed in array, removing final element.': function() {
    var originalArray = [1, 2, 3];
    myPop(originalArray);
    eq(originalArray.length, 2);
  },
  'It should set length of zero if passed an object with no length property.': function() {
    var myObj = {name: 'Alex'};
    myPop(myObj);
    eq(myObj.length, 0);
  },
  'It should update the length of an object that is not an array.': function() {
    var myObj = {length: 2};
    myPop(myObj);
    eq(myObj.length, 1);
  }
})
</script>