Task #2. JS

Pre-requirements

• Participating lecture;
• Basic JS knowledge;
• ES6 Features Knowledge.

Explanation

In this task you will need to create JS utile library to work with arrays and objects.

All code should be written in a single lib.js file. Your library need to be created as a standalone module, so that it can be imported into other projects. In order to make your library usable on any environment, use UMD module pattern.

DISCLAIMER

You're not allowed to use built-in JS-array methods, so each function need to be implementated manually. Any signs of a copy-pasted code from similar utile libs will be considered as a deliberate deception, fully compromising your solution.

The library should provide the following functionality.

Array methods:
map(array, callback)
reduce(array, callback, initialValue)
filter(array, callback)
foreach(array, callback)
take(array, n)
skip(array, n)
some(array, callback)
every(array, callback)
max(array)
min(array)

Object methods:
keys(obj)
values(obj)
pairs(obj)
fromPairs(array)

Here is an example of calling.

libName.take([1, 2, 3, 4], 2) // will return`[1, 2]

The rest of the functions work the same way.

libName.map([1, 2, 3], a => a * 2 ) // will return [2, 4, 6]

After finishing the implementation of these methods, you should implement new chain and value functions, which will allow using the library in the following way.

libName.chain([1, 2, 3]).take(2).skip(1).value(); // will return [2]

Tests

Separate test.js should be filled in with a bunch of examples of usages of your library. Add at least 3 example of calls for each of your methods. No need to use any actual testing frameworks.

Example:

// This function already exists. Feel free to use.
const isEqual = (a = [], b = []) => a.length === b.length && a.every((v, i) => v === b[i]);

...

const testMap = (input, callback, expected) => {
  const actual = libName.map(input, callback);
  console.log(`
    Inputs: ${input}
    Actual: ${actual}
    Expected: ${expected}
    Assess: ${isEqual(actual, expected)}
  `);
};

console.log('[map]: Testing started');
testMap([1,2,3,4], v => v * 2, [2,4,6,8]);
testMap([1,2,3,4], v => v + 2, [3,4,5,6]);
testMap([1,2,3,4], v => v, [1,2,3,4]);
console.log('[map]: Testing done');

Rating criterias

• 5 – Task is completed, solution is clean, readable and reliable. Module can be imported in NodeJS project, React project and used in plain JS-script. All tests are passing;
• 4 – Task is completed, minor edge-cases missed, code is readable and reliable in most cases. Module can be imported in at least one environment. All tests are passing;
• 3 – Task is completed, edge cases missing, code is readable, but has huge gaps in reliability;
• 2 – Partial completion of the tasks, functionality doesn’t fully work or fail on some usual cases;
• 1 – Partial completion of the tasks, unable to run, test;
• 0 – No completion or no submission.