High-order merge function.

merge.js

// High-order merge function.
// Dependency: underscore.js [http://underscorejs.org]
// Demo: http://jsfiddle.net/7HB8J/
// First argument: Function (returns a Boolean, that decides, wether it is the same (hence can be overwritten))
// Rest: Array(s)

merge = function (f) {
  var as = _.flatten(Array.prototype.slice.call(arguments, 1)).reverse().map(function (a) { return {v: a, uniq: 0}; });

  return as.map(function (a) {
    if (a.uniq === 1) return a;
    else {
      a.uniq = 2;

      for (var i in as) if ((as[i].uniq === 0) && (f(a.v, as[i].v))) as[i].uniq = 1;
      return a;
    }
  }).filter(function (a) { return a.uniq === 2; }).map(function (a) { return a.v; });
}