myShift.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>
  // The shift() method removes the first element from an array and returns that removed element. 
    // This method changes the length of the array.

    // The shift method removes the element at the zeroeth index.
    // It shifts the values at consecutive indexes down. 
    // If the length property is 0, undefined is returned.
    // It returns the removed value. 

  // Shift is intentionally generic; this method can be called or applied to array-like objects. 

  // myShift
    // Parameter: an array (or array-like object with length property).
      // input array will be modified - zeroth-index element will be removed.
      // each subsequent element index will be shifted down.
    // Return Value: the zeroth index element from the given array.

  function myShift(arr) {
    if (!Array.isArray(arr) && arr.length === undefined) {
      throw new TypeError('myShift must be passed an array or array-like object');
    }
    var shiftedEl = arr[0]
    for (var i = 1; i < arr.length; i++) {
      arr[i - 1] = arr[i];
    }
    arr.length = (arr.length - 1);
    return shiftedEl;
  }

  tests({
    'It should throw an error if not passed an array or array-like object.': function() {
      var isTypeError = false;
      try {
        myShift({name: 'Alex'});
      } 
      catch(e) {
        isTypeError = (e instanceof TypeError);
      }
      eq(isTypeError, true);
    },
    'It should return the value of array[0].': function() {
      eq(myShift([1]), 1);
    },
    'It should shift each el in array (starting at array[1]) one index lower.': function() {
      var myArray = [1, 2];
      myShift(myArray);
      eq(myArray[0], 2);
    },
    'It should decrease the length of array parameter by 1.': function() {
      myArr = [1, 2, 3];
      myShift(myArr);
      eq(myArr.length, 2);
    },
    'It should work on an array-like object.': function() {
      var shifted = function() {
        var args = arguments;
        var resultEl = arguments[0];
        var resultLength = arguments.length - 1;
        eq(myShift(arguments), resultEl);
        eq(arguments.length, resultLength);
      }
      shifted(1, 2, 3);
    }
  })
</script>