Unique items from Array by calling a method

gistfile1.js

var _ = require('lodash');
var fp = require('functional-pipeline');

var items = [{
  toString: function () {
    return 'foo';
  }
}, {
  toString: function () {
    return 'bar';
  }
}, {
  toString: function () {
    return 'foo';
  }
}];
var result = _.unique(items, fp('toString'));
// same as
result = _.unique(items, function (item) {
  return item.toString();
});