[Algorithms] Tree Data Structure in JavaScript

In a tree, nodes have a single parent node and may have many children nodes. They never have more than one parent nor point to any siblings.

The most common tree structure you see is a web page. The underlying structure is often called the "DOM tree". The html element forms the root of our tree, with children of head and body, so on and so forth. In this lesson, we'll create a quick example of a DOM tree with our tree data structure.

 

function crateNode (key) {
    let children = [];
    return {
        key,
        children,
        addChild (cKey) {
            const childNode = crateNode(cKey)
            this.children.push(childNode)
            return childNode;
        }
    }
}

function createTree (rootKey) {
    const root = crateNode(rootKey);

    function print () {
        let result = '';

        function traverse (node, visitFn, depth) {
            visitFn(node, depth);

            if (node.children.length) {
                node.children.forEach(n => traverse(n, visitFn, depth + 1))
            }
        }

        function addKeyToResult(node, depth) {
            result +=
              result.length === 0
                ? node.key
                : `
${' '.repeat(depth * 2)}${node.key}`
        }

        traverse(root, addKeyToResult, 0)

        return result;
    }
    return {
        root,
        print
    }
}

const dom = createTree('html')
const head = dom.root.addChild('head')
const body = dom.root.addChild('body')
const title = head.addChild('title - egghead Tree Lesson')
const header = body.addChild('header')
const main = body.addChild('main')
const footer = body.addChild('footer')
const h1 = header.addChild('h1 - Tree Lesson')
const p = main.addChild('p - Learn about trees!')
const copyright = footer.addChild(`Copyright ${new Date().getFullYear()}`)

console.log(dom.print())

/*
html
  head
    title - egghead Tree Lesson
  body
    header
      h1 - Tree Lesson
    main
      p - Learn about trees!
    footer
      Copyright 2018

*/