Iteratively merge arrays, preserving relative order

mergeArrays.js

/**
 * This seems like a problem which can be solved more elegantly, but I needed this code today
 * so despite a strong urge to sit down with pen and paper and relive my Godel, Escher, Bach days
 * I must instead move along for now.
 * 
 * 
 */
 
!function() {
  
  /**
   * Merge two arrays, maintaining order as much as possible
   */
  function mergeArrays(left, right) {
    var result = [],
        leftItem, rightItem,
        leftIdx, rightIdx;

    /**
     * Early out for invalid arguments
     * doesn't check type
     */
    if (!left || !right || (!left.length && !right.length)) {
      return result;
    }

    /**
     * Special case to iteratively reduce
     */
    if (arguments.length > 2) {
      right = mergeArrays.apply(this, Array.prototype.slice.call(arguments, 1));
    }
    
    // first add any data which precedes the first entry of left (ie. prepended to reference)
    leftItem = left[0];
    rightIdx = right.indexOf(leftItem);
    if (rightIdx !== -1) {
      result = result.concat( right.slice(0, rightIdx) );   
      right = right.slice(rightIdx);
    }
    
    // scan for matches
    for (var i=0, max=left.length; i < max && right.length !== 0; i++) {
      leftItem = left[i];
      rightItem = right[0];

      // same? simply insert
      if (leftItem === rightItem) {
        result.push(leftItem);
        right = right.slice(1);
        continue;
      }
      
      // otherwise, if it doesn't exist, simply add it
      rightIdx = right.indexOf(leftItem);
      if (rightIdx === -1) {
        result.push(leftItem);
        continue;
      }
      
      // otherwise inject whatever exists until that point, skipping
      // anything which exists in the left
      for (var j=0; j < rightIdx; j++) {
        var rightItem = right[j];
        var leftIdx = left.indexOf(rightItem);
        if (leftIdx === -1) {
          result.push(rightItem);
        }
      } 
      right = right.slice(rightIdx);
      // at this stage we don't actually want to step forward on the left array
      i--; 
    }
    
    // finally add any appended data from right
    result = result.concat( right );
    
    return result;
  }
  
  var first = [
    'hello',
    'foghorn',
    'does not exist in second',
    'leghorn'
  ];
  var second = [
    'prepended',
    'hello', 
    'inserted first',
    'foghorn',
    'inserted second',
    'inserted more',
    'leghorn',
    'appended'
  ];
  var third = [
    'inserted first',
    'chickens',
    'inserted more',
    'appended',
    'extra',
    'stuff'
  ];
  
  var test = mergeArrays(first, second, third);
  console.log(test);
}();