Memoize

memoize1.js

const getCommaDelimitedKeys = memoize(object => {
 return Object.keys(object).join(",");
});

const fruits = {
  apple: 95,
  avocado: 234,
  banana: 133
};

// apple,avocado,banana
console.log(getCommaDelimitedKeys(fruits));
console.log(getCommaDelimitedKeys(fruits));

memoize2.js

const getCommaDelimitedKeys = memoize((...objects) => {
 const allUniqueKeys = objects.reduce((allUniqueKeys, object) => {
   Object.keys(objectKeys).forEach(key => {
     if (allUniqueKeys.indexOf(key) === -1) {
       allUniqueKeys.push(key);
     }
   });
   return allUniqueKeys;
 }, [])
 
 return allUniqueKeys.join(",");
});

memoize3.js

const getCommaDelimitedKeys = memoize((...objects) => {
 const allUniqueKeys = objects.reduce((allUniqueKeys, object) => {
   Object.keys(objectKeys).forEach(key => {
     if (allUniqueKeys.indexOf(key) === -1) {
       allUniqueKeys.push(key);
     }
   });
   return allUniqueKeys;
 }, [])
 
 return allUniqueKeys.join(",");
}, (...objects) => {
  return objects.reduce((allIds, object) => {
    allIds.push(object.id);
    return allIds;
  }, []);
});