provectus/internship

internship's Issues

grouping todos by users func

/*

• // 1. grouping todos by users:
• https://github.com/gagan-bansal/json-groupby - lib implementing grouping functionality
• book : Бэнкс Алекс, Порселло Ева React и Redux: функциональная веб-разработка «O’Reilly», chapter 3
• https://24ways.org/2019/five-interesting-ways-to-use-array-reduce/
  */
  var selectGrpUserId = function (todos_by_userid) {
  return todos_by_userid.reduce( function (res, cur) {
  const { userId, id, title, completed } = cur;
  // initialaze if undefined:
  if (!res[userId])
  res[userId] = [];
  res[userId].push({id, title, completed, userId}); // push all + UserId to check for correctness
  //res[userId].push(id); // or push only id
  return res;
  }, {})
  };

const url = "https://jsonplaceholder.typicode.com/todos";
// some experiments on my own with chaining (thenable):
const selectTodosByUserId = async (id) =>
await fetch(url)
.then((response) => response.json())
.then(selectGrpUserId)
.then(function (res) { return res[id] });

selectTodosByUserId(2).then((res) => {
console.log(res);
});

(possible) solution for wrapper func for any selector (promise in fact) func with memoize

/*

• Optional: 3. Write a helper function which
• 1. acts like a wrapper
• 2. memoizes the result of any selector function:
• resources used:
• https://stackoverflow.com/questions/48449748/how-to-write-a-javascript-promise-decorator
• "JavaScript Patterns" by Stoyan Stefanov (c) O’Reilly - for memorization func
  */

const Wrapper_With_Memoization_and_Timing = (promiseFn, ...args) => {

const start = Date.now()
return promiseFn(...args).then(result => {
// console.log(Promise in \"%s(%d)\" finished in ${(Date.now() - start) / 1000} seconds, promiseFn.name, ...args);

// deal with cache key:
// minor modification: using memoiz array with unique indices composed of promiseFn.name and its args:
var cachekey = [promiseFn.name, ...args];
console.log("cache key: ", cachekey);

// deal with cache value:
if (!Wrapper_With_Memoization_and_Timing.cache[cachekey]) {
console.log("NOT FOUND in cache, memorizing the result.");
Wrapper_With_Memoization_and_Timing.cache[cachekey] = result;
}
else {
console.log("FOUND in cache, return memorized result.");
}
//console.log(Wrapper_With_Memoization_and_Timing.cache);
return Wrapper_With_Memoization_and_Timing.cache[cachekey];
}, error => {
console.log(Promise errored in ${(Date.now() - start) / 1000} seconds)
return Promise.reject(error)
})
};
Wrapper_With_Memoization_and_Timing.cache = {};

setTimeout(() =>
{
console.log("Hello world with memo!", Wrapper_With_Memoization_and_Timing.cache["selectById,2"]);
//for (let i in Wrapper_With_Memoization_and_Timing.cache)
// console.log("Hello world in sync!", Wrapper_With_Memoization_and_Timing.cache[i], i, typeof i);
}
, 5000);

// some experiments on my own...
var mf = function ( ) {
// run some tests:
Wrapper_With_Memoization_and_Timing(selectById, 1);
Wrapper_With_Memoization_and_Timing(selectById, 1);
Wrapper_With_Memoization_and_Timing(selectById, 2);
Wrapper_With_Memoization_and_Timing(selectById, 2);
Wrapper_With_Memoization_and_Timing(selectAll);
Wrapper_With_Memoization_and_Timing(selectAll);
}( );

//console.log("this is a last line of the script.");

/* sync call not implemented yet (MK)

• still yet to write it properly...
  for (let i in Wrapper_With_Memoization_and_Timing.cache)
  console.log("Hello world in sync!", Wrapper_With_Memoization_and_Timing.cache[i]);
  */
  // console.log("Hello world in sync!", Wrapper_With_Memoization_and_Timing.cache["selectById, 1"]);

overall solution for task #2 frontend internship test assignment

An overall solution for task №2 test assignment here is a link to typescript pg. it comes with types, class and memoization