Partial functions in Javascript with bind

bind.js

var cities = [{name: "Paris", country: "France"}, {name: "London", country: "UK"}, {name: "Rome", country: "Italy"},{name: "Manchester", country: "UK"}];

var isIn = function(country, city) {
  return city.country === country;
};

isIn("UK", {name: "London", country: "UK"}); //true

var UKCity = isIn.bind(null, "UK");//don't need to set the this keyword, just passing null
//UKCity can be used like this:
UKCity({name: "London", country: "UK"}); //true

//UKCity is now a perfect fit to be used with a higher order function
var UKCities = cities.filter(UKCity);
//UKCities === [{name: "London", country: "UK"}, {name: "Manchester", country: "UK"}]

//get the list of the Italian cities is as simple as:
cities.filter(isIn.bind(null, "Italy")); 
//[{name: "Rome", country: "Italy"}]