ES6 utils for arrays and objects

util.js

function collapse (arr) {
  return [...new Set(arr)];
}

function isIterable(obj) {
  return obj != null && typeof obj[Symbol.iterator] === 'function';
}

function collapseAll (...args) {
  const all = args.reduce((arr, arg) => {
    return isIterable(arg) ? arr.concat(...arg) : arr;
  }, []);
  return collapse(all)
}

function collapseKeys (...args) {
  return collapseAll(
    ...args.map(obj => obj && Object.keys(obj))
  )
}

function mergeByKey(...args){
  return collapseKeys(...args).reduce((result, key) => {
    result[key] = collapseAll(obj1[key], obj2[key]);
    return result;
  }, {});
}