myJoin.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>
  // The join() method joins all elements of an array (or an array-like object) into a string and returns this string.
  // Parameters
    // separator (Optional)
      // Specifies a string to separate each pair of adjacent elements of the array. 
      // The separator is converted to a string if necessary. => VERY CONFUSING LINE FROM DOCS.
        // numbers and are converted to strings.
        // null and NaN convert to strings
        // letters and symbols throw an error if not previously defined.
        // undefined defaults to a comma.
      // If omitted, the array elements are separated with a comma (","). 
      // If separator is an empty string, all elements are joined without any characters in between them.
  // Return value
    // A string with all array elements joined. If arr.length is 0, the empty string is returned.

  // Notes:
    // If an element is undefined or null, it is converted to the empty string.
  
  function myJoin(array, separator) {
    var returnValue = '';
    if (array.length === 0) {
      return returnValue;
    }
    for (var i = 0; i < array.length; i++) {
      var originalEl = array[i];
      if (originalEl === undefined || originalEl === null) {
        originalEl = '';
      }

      var stringEl = originalEl.toString();

      if ((arguments.length < 2 || arguments[1] === undefined) && i < array.length - 1) {
        stringEl = stringEl + ',';
      }
      if (arguments.length === 2 && i < array.length - 1) {
        stringEl = stringEl + separator;
      }
      returnValue += stringEl;
    }
    return returnValue;
  }

  tests({
    'It should return an empty string if passed an empty array.': function() {
      var empty = myJoin([]);
      eq(empty, '');
    },
    'It should default separator to a comma if not passed a separator.': function() {
      var joined = myJoin(['Alex', 'Katie']);
      eq(joined.charCodeAt(4), '44');
    },
    'It should separate string elements with the separator if provided.': function() {
      var myArray = ['Alex', 'Katie'];
      var joined = myJoin(myArray, ':');
      eq(joined.charCodeAt(4), 58);
    },
    'It should use default comma if passed undefined as separator.': function() {
      var joined = myJoin(['Alex', 'Katie'], undefined);
      eq(joined.charCodeAt(4), '44');
    },
    'If separator is an empty string, all elements should be joined with no spaces.': function() {
      var joined = myJoin(['Alex', 'Katie'], '');
      eq(joined.charCodeAt(4), 75);
    },
    'It should convert undefined/null elements to an empty string.': function() {
      var undefinedEls = myJoin([undefined, null]);
      eq(myJoin(0), '');
      eq(myJoin(1), '');
    },
    'If passed an array containing one comma (one hole), it should delete this trailing comma and return an empty string.': function() {
      var myArray = [,];
      var joined = myJoin(myArray);
      eq(joined, '');
    }
  })
</script>