Building tree array of objects from flat array of objects [duplicate]

Answer 1

Iterate with Array#reduce and a helper object:

var nodes = [
  {id: 1, pid: 0, name: "kpittu"},
  {id: 2, pid: 0, name: "news"},
  {id: 3, pid: 0, name: "menu"},
  {id: 4, pid: 3, name: "node"},
  {id: 5, pid: 4, name: "subnode"},
  {id: 6, pid: 1, name: "cace"}
];

const helper = nodes.reduce((h, o) => (h[o.id] = Object.assign({}, o), h), Object.create(null));

const tree = nodes.reduce((t, node) => {
  const current = helper[node.id];
  
  if(current.pid === 0) { // if it doesn't have a parent push to root
    t.push(current);
  } else {
    helper[node.pid].children || (helper[node.pid].children = []) // add the children array to the parent, if it doesn't exist
    helper[node.pid].children.push(current); // push the current item to the parent children array
  }
  
  return t;
}, []);

console.log(tree);