in src/utils/union.js [8:20]
module.exports = function(arrays) {
const result = new Set(arrays[0]);
let i,j, array;
for (i = 1; i < arrays.length; i++) {
array = arrays[i];
for (j = 0; j < array.length; j++) {
result.add(array[j]);
}
}
return Array.from(result);
};