http://www.freecodecamp.com/tylerl-uxai 's solution for Bonfire: Where art thou

bonfire-where-art-thou.js

// Bonfire: Where art thou
// Author: @tylerl-uxai
// Challenge: http://www.freecodecamp.com/challenges/bonfire-where-art-thou
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function where(collection, source) {
// speed test
  var keys = Object.keys( source ); // returns the keys to the variable
  
  return collection.filter(function(propertiesForEachKey){
    for (var i = 0; i< keys.length; i++){
      if(!propertiesForEachKey[keys[i]] || source[keys[i]] !== propertiesForEachKey[keys[i]]){
        return false;
      }
    }
    return true;
  });
}

where([{ first: "Romeo", last: "Montague" }, { first: "Mercutio", last: null }, { first: "Tybalt", last: "Capulet" }], { last: "Capulet" });