nesting parent-child using recursion

Question

I have json object like this

[
{"id" : 1, "parentid" : null},
{"id" : 2, "parentid" : null},
{"id" : 3, "parentid" : 2},
{"id" : 4, "parentid" : 3}
]

I want to make it nested like this in javascript

[
{"id" : 1, "parentid" : null},
{"id" : 2, "parentid" : null, "childs": 
   [{"id" : 3, "parentid" : 2, "childs": 
     [{"id": 4, "parentid" : 3}]}]
}
]

Do I need to use recursion function or just a simple loop will do it? What is the most efficient way to achieve it?

Answer 1

You have to use recursive function for this. Simple loop will not work, because there can be n number of objects in an array and upto n level. Here is a function that you can utilize

var a = [{
    "id": 1,
    "parentid": null
  },
  {
    "id": 2,
    "parentid": null
  },
  {
    "id": 3,
    "parentid": 2
  },
  {
    "id": 4,
    "parentid": 3
  }
]


function getNestedChildren(arr, parent) {
    var out = []
    for(var i in arr) {
        if(arr[i].parentid == parent) {
            var children = getNestedChildren(arr, arr[i].id)

            if(children.length) {
                arr[i].children = children
            }
            out.push(arr[i])
        }
    }
    return out
}

console.log(getNestedChildren(a))

Link: http://oskarhane.com/create-a-nested-array-recursively-in-javascript/