Create a flat list of nodes from a nested tree structure.

tree_to_list_nodes.js

// nestedTree is a tree structure containing subtrees under "nodes" property. d=1 is the default "depth of the tree"
function flatDeep(arr, d = 1) {
    return d > 0 ? arr.reduce((acc, val) => acc.concat(Array.isArray(val.nodes) ? flatDeep(val.nodes, d - 1) : val), [])
                 : arr.slice();
 };

let flat = flatDeep(nestedTree, Infinity);
// Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat