JavaScript: Nest a given flat array of objects linked to one another recursively

JavaScript fundamental (ES6 Syntax): Exercise-90 with Solution

Nest Flat Array Recursively

Write a JavaScript program to nest a given flat array of objects linked to one another recursively.

Note: Useful for nesting comments, such as the ones on reddit.com.

• Use recursion.
• Use Array.prototype.filter() to filter the items where the id matches the link.
• Use Array.prototype.map() to map each item to a new object that has a children property which recursively nests the items based on which ones are children of the current item.
• Omit the second argument, id, to default to null which indicates the object is not linked to another one (i.e. it is a top level object).
• Omit the third argument, link, to use 'parent_id' as the default property which links the object to another one by its id.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2
// Define the 'nest' function to create a nested structure from flat data based on parent-child relationships.
const nest = (items, id = null, link = 'parent_id') =>
  items
    .filter(item => item[link] === id)
    .map(item => ({ ...item, children: nest(items, item.id) }));

// Example usage:
// Given a flat array of comments with parent-child relationships, create a nested structure.
const comments = [
  { id: 1, parent_id: null },
  { id: 2, parent_id: 1 },
  { id: 3, parent_id: 1 },
  { id: 4, parent_id: 2 },
  { id: 5, parent_id: 4 }
];
const nestedComments = nest(comments); 
console.log(nestedComments);

Output:

[{"id":1,"parent_id":null,"children":[{"id":2,"parent_id":1,"children":[{"id":4,"parent_id":2,"children":[{"id":5,"parent_id":4,"children":[]}]}]},{"id":3,"parent_id":1,"children":[]}]}]

Flowchart:

Live Demo:

See the Pen javascript-fundamental-exercise-90 by w3resource (@w3resource) on CodePen.

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