javascript - TypeError: Cannot read property 'data' of undefined - but it is defined - Stack Overflow

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I am working on a binary search tree algorithm and for some reason, I keep getting a type error. It always occurs when a second value is being inserted into the tree. Specifically when the current node's value is being pared to the ining data value

Here's the code:

class Node {
    constructor(data, left = null, right = null) {
        this.data = data;
        this.leftNode = left;
        this.rightNode = right;
    }
}

class BST {
    constructor() {
        this.root = null;
    }
    insert(data) {
        const dataNode = new Node(data);
        if (this.root === null) {
            this.root = dataNode;
        } else {
            let currentNode = this.root;
            let parentNode;
            while (true) {
                parentNode = currentNode;
                if (data < currentNode.data) {
                    currentNode = parentNode.left;
                    if (parentNode.left === null) {
                        parentNode.left = dataNode
                        break;
                    }
                } else {
                    currentNode = parentNode.right
                    if (parentNode.right === null) {
                        parentNode.right = dataNode
                        break;
                    }
                }
            }
        }
    }
}
const bst = new BST();

bst.insert(10);
bst.insert(5);
bst.insert(6);
bst.insert(8);
bst.insert(12);
bst.insert(7);
bst.insert(7);

I am working on a binary search tree algorithm and for some reason, I keep getting a type error. It always occurs when a second value is being inserted into the tree. Specifically when the current node's value is being pared to the ining data value

Here's the code:

class Node {
    constructor(data, left = null, right = null) {
        this.data = data;
        this.leftNode = left;
        this.rightNode = right;
    }
}

class BST {
    constructor() {
        this.root = null;
    }
    insert(data) {
        const dataNode = new Node(data);
        if (this.root === null) {
            this.root = dataNode;
        } else {
            let currentNode = this.root;
            let parentNode;
            while (true) {
                parentNode = currentNode;
                if (data < currentNode.data) {
                    currentNode = parentNode.left;
                    if (parentNode.left === null) {
                        parentNode.left = dataNode
                        break;
                    }
                } else {
                    currentNode = parentNode.right
                    if (parentNode.right === null) {
                        parentNode.right = dataNode
                        break;
                    }
                }
            }
        }
    }
}
const bst = new BST();

bst.insert(10);
bst.insert(5);
bst.insert(6);
bst.insert(8);
bst.insert(12);
bst.insert(7);
bst.insert(7);

Here's the error:

Uncaught TypeError: Cannot read property 'data' of undefined
    at BST.insert (<anonymous>:22:32)
    at <anonymous>:42:5

• javascript
• binary-search-tree
• typeerror
• graph-algorithm

Share Improve this question Follow edited Sep 22, 2018 at 18:57 VLAZ 29.1k99 gold badges6262 silver badges8484 bronze badges asked Sep 22, 2018 at 18:54 AlsidneioAlsidneio 3311 silver badge55 bronze badges

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3 Answers 3

Sorted by: Reset to default 6

you are doing parentNode.left which is undefined while you should do parentNode.leftNode

It seems you assigned parent.left to currentNode before you assign any value to parentNode.left This also happened for right one.

You had a typo. Fixed snippet below:

class Node {
  constructor(data, left = null, right = null) {
    this.data = data;
    this.left = left;
    this.right = right;
  }
}

class BST {
  constructor() {
    this.root= null;
  }
 insert(data) {
    const dataNode = new Node(data);
    if (this.root === null) {
      this.root = dataNode;
    } else {
      let currentNode = this.root;
      let parentNode;
      while (true) {
        parentNode = currentNode;
        if (data < currentNode.data) {
          currentNode = parentNode.left;
          if (parentNode.left === null) {
            parentNode.left = dataNode;
            break;
          }
        } else {
          currentNode=parentNode.right
          if (parentNode.right === null) {
            parentNode.right = dataNode;
            break;
          }
        }
      }
    }
  }
}

const bst = new BST();

bst.insert(10);
bst.insert(5);
bst.insert(6);
bst.insert(8);
bst.insert(12);
bst.insert(7);
bst.insert(7);

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