How to convert a nested array with parent child relationship to a plain array?

Question

I have an array with nested objects having parent-child relationship like so:

[
{id: 1, title: 'hello', parent: 0, children: [
    {id: 3, title: 'hello', parent: 1, children: [
        {id: 4, title: 'hello', parent: 3, children: [
            {id: 5, title: 'hello', parent: 4, children: []},
            {id: 6, title: 'hello', parent: 4, children: []}
        ]},
        {id: 7, title: 'hello', parent: 3, children: []}
    ]}
]},
{id: 2, title: 'hello', parent: 0, children: [
    {id: 8, title: 'hello', parent: 2, children: []}
]}
]

I need to convert it into a plain array retaining the parent child relationship like so and in the order of parent and all its children returned first before proceeding on to the next parent.

[
{id: 1, title: 'hello', parent: 0},
{id: 3, title: 'hello', parent: 1},
{id: 4, title: 'hello', parent: 3},
{id: 5, title: 'hello', parent: 4},
{id: 6, title: 'hello', parent: 4},
{id: 7, title: 'hello', parent: 3},
{id: 2, title: 'hello', parent: 0},
{id: 8, title: 'hello', parent: 2}
]

I was able to convert the other way round with a recursive function.

But I need to do the opposite in an efficient way. There is multilevel nesting as shown in the sample nested array.

EDIT: Updated the nested array to have an empty children array for leaf nodes.

And also, an answer in ES5 would help.

Answer 1

I just use a simple recursive function to make an array object into a plain array

var arr = [ {id: 1, title: 'hello', parent: 0, children: [ {id: 3, title: 'hello', parent: 1, children: [ {id: 4, title: 'hello', parent: 3, children: [ {id: 5, title: 'hello', parent: 4, children: []}, {id: 6, title: 'hello', parent: 4, children: []} ]}, {id: 7, title: 'hello', parent: 3, children: []} ]} ]}, {id: 2, title: 'hello', parent: 0, children: [ {id: 8, title: 'hello', parent: 2, children: []} ]} ];

var result = [];
var convertArrToObj = (arr) => {
  arr.forEach(e => {
    if (e.children) {
      result.push({
        id: e.id,
        title: e.title,
        parent: e.parent
      });
      convertArrToObj(e.children);
    } else result.push(e);

  });
};
convertArrToObj(arr);
console.log(result);