Intersection and contains - stripped from underscore

contains

function contains(a, obj) {
    var i = a.length;
    while (i--) {
       if (a[i] === obj) {
           return true;
       }
    }
    return false;
}

intersection

function intersection(list) {
  if( list == null ) return [];
  var result = [], set = list[0];
  var setsLength = list.length;
  for( var i = 0, length = set.length; i < length; i++ ) {
    var item = set[i];
    if( contains(result, item) ) continue;
    for( var j = 1; j < setsLength; j++ )  {
      if( !contains(list[j], item) ) break;
    }
    if( j === setsLength ) result.push( item );
  }
  return result;
}