function whatIsInAName(collection, source) {

var sK = Object.keys(source);

return collection.filter(x => sK.every(y => x[y] === source[y]));

}

/*

function whatIsInAName(collection, source) {

var sourceKey = Object.keys(source);

return collection.filter(function (x) {

return sourceKey.every(function (y) {

return x[y] === source[y];

});

}

);

}

*/

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

// should return [{ first: "Tybalt", last: "Capulet" }].

whatIsInAName([{ "a": 1 }, { "a": 1 }, { "a": 1, "b": 2 }], { "a": 1 });

// should return [{ "a": 1 }, { "a": 1 }, { "a": 1, "b": 2 }].

whatIsInAName([{ "a": 1, "b": 2 }, { "a": 1 }, { "a": 1, "b": 2, "c": 2 }], { "a": 1, "b": 2 });

// should return [{ "a": 1, "b": 2 }, { "a": 1, "b": 2, "c": 2 }].

whatIsInAName([{ "a": 1, "b": 2 }, { "a": 1 }, { "a": 1, "b": 2, "c": 2 }], { "a": 1, "c": 2 });

// should return [{ "a": 1, "b": 2, "c": 2 }].