[array] array utils #utils

array.js

function duplicate(arr){
  let set = new Set();
  let result = [];
  for(let i = 0;i < arr.length; ++i) {
    if(!set.has(arr[i])) result.push(arr[i]);
    set.add(arr[i]);
  }
  return result;
}

// flat list to tree, eg:
// [{id:1, parentId: 0}, {id: 2, parentId: 1}, {id: 3, parentId: 0}, {id: 4, parentId: 2}] =>
// [{id:1, parentId: 0, children: [{id: 2, parentId: 1, children: [{id: 4, parentId: 2}]}]}, {id: 3, parentId: 0}]
function flatToTree(arr, idProp, parentIdProp, childrenProp = 'children'){
  function flatItemToTree(arr, item) {
    let subItems = arr.filter(subitem => subitem[parentIdProp] === item[idProp]);
    subItems.forEach(subitem => isIter.add(subitem[idProp]));
    let subTrees = subItems.map(item => flatItemToTree(arr, item));
    return Object.assign({}, item, {[childrenProp]: subTrees});
  }
  
  if (!idProp || !parentIdProp) return arr;
  
  let isIter = new Set();
  let result = [];
  arr.forEach(item => {
    let id = item[idProp];
    if (!isIter.has(id)) {
    	result.push(flatItemToTree(arr, item));
    }
  });
  return result;
}