In an old post called Create a nested array recursively in Javascript I wrote how to go from

[
    {id: 1, title: 'hello', parent: 0},
    {id: 2, 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: 8, title: 'hello', parent: 2}
]

to

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

with a recursive Javascript function.

I’ve been asked to show how to do this in Coffeescript.

getNestedChildren = (arr, parent) ->
  out = []
  for item in arr
    continue unless item.parent is parent
    children = getNestedChildren arr, item.id    
    item.children = children if children.length
    out.push item
  out

which compiles to this Javascript:

var getNestedChildren;

getNestedChildren = function(arr, parent) {
  var children, item, out, _i, _len;
  out = [];
  for (_i = 0, _len = arr.length; _i < _len; _i++) {
    item = arr[_i];
    if (item.parent !== parent) {
      continue;
    }
    children = getNestedChildren(arr, item.id);
    if (children.length) {
      item.children = children;
    }
    out.push(item);
  }
  return out;
};

On js2coffee you can convert Javascript to and form Coffeescript.