Collection comparison helpers

collection-compare.js

function allInCollection (collection) {
  return function (subCollection) {
    return subCollection.every(function (subItem) {
      return collection.some(function (item) {
        return item.id === subItem.id;
      });
    });
  };
}

function inCollection (collection) {
  return function (compItem) {
    return collection.some(function (item) {
      return item.id === compItem.id;
    });
  };
}