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JS - Basic Tree Data Structure


Tree Data Structure

A tree is a non hierarchical data structure in which the the information or value is represented by Tree Nodes and these nodes are connected by Edges.

Tree Terminologies
  • Node: A node is a entity which holds a value, an information, a pointer, etc.

    • Internal Node: A node which has at least one child
    • Leaf Node: A node which has no child or the last node in a tree branch

  • Edge: Edge is the link in between two nodes

  • Root Node: The entry point (usually represented by topmost node) of a tree is known as root node.

  • Height: Number of the edges in the longest path from root node to leaf node.

  • Degree: Degree of a node is the total number of branches of that node

Types of Tree

Tree is of 4 types:

  1. Binary Tree
  2. Binary Search Tree
  3. AVL Tree
  4. B-Tree
Tree Traversal

To perform any operation or to get a specific value, tree traversal algorithms are used. We can traverse tree in basically three following types:

  1. Preorder Traversal
  2. Inorder Traversal
  3. Post Traversal
Creating a Basic Tree

Here is an example of a tree which we are going to implement at last

a tree with 7 nodes Figure 1: An example of a tree

First we need to create the JS class

                                    $dy> class Tree {
                                    $dy>     // Tree defination will come here
                                    $dy> }

A tree node contains value, left child and right child so let's go create that

                                    $dy> class Tree {
                                    $dy>     constructor(nodeValue, leftNode, rightNode) {
                                    $dy>         this.value = nodeValue;
                                    $dy>         this.leftNode = leftNode;
                                    $dy>         this.rightNode = rightNode;
                                    $dy>     }
                                    $dy> }

Assign default parameter as null if user doesn't pass the pointer to the left or right node

                                    $dy> // Replace constructor signature with the following
                                    $dy> constructor(nodeValue = 0, leftNode = null, rightNode = null)

Let's create a tree with three nodes

                                    $dy> // we need not pass left or right as default parameter are already there
                                    $dy> const left = new Tree('left');
                                    $dy> const right = new Tree('right');
                                    $dy> // here we need to pass the left and right node as parameter
                                    $dy> const root = new Tree('root', left, right);

That's it, you have created the tree in above step and here is the complete code for a tree

                                    $dy> class Tree {
                                    $dy>     constructor(nodeValue, leftNode, rightNode) {
                                    $dy>         this.value = nodeValue;
                                    $dy>         this.leftNode = leftNode;
                                    $dy>         this.rightNode = rightNode;
                                    $dy>     }
                                    $dy> }
                                $dy> const node7 = new Tree(7);
                                $dy> const node6 = new Tree(6);
                                $dy> const node5 = new Tree(5);
                                $dy> const node4 = new Tree(4);
                                $dy> const node3 = new Tree(3, node6, node7);
                                $dy> const node2 = new Tree(2, node4, node5);
                                $dy> const root = new Tree(1, node2, node3);
                <div class="step">
                    <p>Here is the JSON of the tree we just created</p>
                    <div class="code-wrapper">
                                $dy> {
                                $dy>     "value": 1,
                                $dy>     "leftNode": {
                                $dy>         "value": 2,
                                $dy>         "leftNode": {
                                $dy>             "value": 4
                                $dy>         },
                                $dy>         "rightNode": {
                                $dy>             "value": 5
                                $dy>         }
                                $dy>     },
                                $dy>     "rightNode": {
                                $dy>         "value": 3,
                                $dy>         "leftNode": {
                                $dy>             "value": 6
                                $dy>         },
                                $dy>         "rightNode": {
                                $dy>             "value": 7
                                $dy>         }
                                $dy>     }
                                $dy> }
        <section class="main-section" id="Tree_Application">
            <header class="section-header">Tree Application</header>
            <div class="section-content">
                    <li>In searching algorithm, specially in heap sort</li>
                    <li>HTML DOM is a tree</li>
                    <li>Compilers uses the syntax tree to validate the syntax of a code</li>

    // fixing the test suite for the project
    const projectName = 'technical-docs-page';

     * > can assign the whole PRE TAG TEXT through JS
     * > can also use <br /> and &nbsp; to create the pre tag
     * here I am using $dy> to remove the whiteSpace
     * > it won't remove the whiteSpace from the user entered code
     * > it removes only HTML formatter pre tag issues

    const allPreTag = document.querySelectorAll('pre');
    for(let pre of allPreTag) {
        let text = pre.innerText;
        const whiteSpaceLength = text.length - text.trimStart().length;
        let replaceString = "$dy>";
        for(let i = 0; i < whiteSpaceLength; i++) {
            replaceString = " " + replaceString;
        while(text.indexOf(replaceString) !== -1) {
            text = text.replace(replaceString, "");
        pre.innerText = text;
<!-- Remove below comment to add the test-suite script -->
<!-- <script src=""></script> -->

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