function where(collection, source) {

   var arr = [];

   var keys = Object.keys(source);

   arr = collection.filter(function(item){

     for (var i = 0; i < keys.length; i++) {

       if ( !item.hasOwnProperty(keys[i]) || item[keys[i]] !== source[keys[i]]) {

         return false;

       }

     }

     return true;

   });

   // What's in a name?

   return arr;

 }

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