shift.html

<script src="../simpleTest.js"></script>
<script>

// MDN Definition:
// The shift() method removes the first element from an array and 
// returns that removed element. This method changes the length 
// of the array.

// NOTES:

// shift REQUIREMENTS:

// DONE It should return the first element in the array.
// DONE It should make the array shorter.
// DONE It should delete the first index in the array.
// DONE It should shift each value in the array down an index.
// DONE If array is empty, it should return undefined.




function shift(array) {
  var shiftedElement = array[0];
  var bucket = array;

  if (typeof arguments[0] !== 'object') {
    throw new TypeError('array.shift is not a function');
  }

  if (array.length < 1) {
    return undefined;
  }
  
  for (var i = 0; i < array.length - 1; i++) {
    array[i] = bucket[i + 1];
  }
  array.length = array.length - 1;
  return shiftedElement;
}


tests({

  'It should return the first element in the array.': function() {
    var myArray = ['shift', 'keep'];
    var result = shift(myArray);
    eq(result, 'shift');
  },
  'It should make the array shorter.': function() {
    var myArray = ['shift', 'keep'];
    eq(myArray.length, 2);
    shift(myArray);
    eq(myArray.length, 1);
  },
  'It should delete the first index in the array.': function() {
    var myArray = ['shift', 'keep'];
    eq(myArray[0], 'shift');
    shift(myArray);
    eq(myArray.includes('shift'), false);
  },
  'It should shift each value in the array down an index.': function() {
    var myArray = ['shift', 'keep'];
    eq(myArray[1], 'keep');
    shift(myArray);
    eq(myArray[0], 'keep');
  },
  'If array is empty, it should return undefined.': function() {
    var myArray = [];
    var result = shift(myArray);
    eq(result, undefined);
  },
  'If it is called on an element that is not an array, throw TypeError.': function() {
    var myElement = 2;
    var isTypeError = false;
    try {
      shift(myElement);
    } catch(e) {
      isTypeError = (e instanceof TypeError);
    }
    eq(isTypeError, true);
  }
});
</script>