join.js

'use strict';

var concatArrays = function (arrays) {
    let concatedArray = [];

    arrays.forEach(array => {
        concatedArray = concatedArray.concat(array);
    });

    return concatedArray;
}

var isDuplicate = function (a, b) {
    return a === b;
}

var findDuplicatesIndexes = function (originalIndex, array) {
    let duplicatesIndexes = [];

    for (let i = (originalIndex + 1); i < array.length; i++) {
        if (isDuplicate(array[originalIndex], array[i])) {
            duplicatesIndexes.push(i);
        }
    }

    return duplicatesIndexes;
}

var removeDuplicatedIndexes = function (array, indexes) {
    if (!indexes.length) {
        return array;
    }

    let localArray = Array.from(array);

    indexes.reverse();
    indexes.forEach(index => localArray.splice(index, 1));

    return localArray;
}

var removeDuplicates = function (array) {
    let localArray = Array.from(array)

    for (let i = 0; i < (localArray.length - 1); i++) {
        let duplicates = findDuplicatesIndexes(i, localArray);
        localArray = removeDuplicatedIndexes(localArray, duplicates);
    }

    return localArray;
}

function newestLastModified (a, b) {
    return a.lastModified >= b.lastModified;
}

module.exports = function (...arrays) {
    if (arrays == null) {
        return [];
    }

    let joined = concatArrays(arrays);
    let withoutDuplicates = removeDuplicates(joined);
    let sortedArrays = withoutDuplicates.sort(newestLastModified);

    return withoutDuplicates;
};