I am creating a bubble sort visualizer using html, css and javascript. Following is the javascript code:

const numbers = [];
let targetParent = document.querySelector("#bars")

function swap(el1, el2) {
    const style1 = window.getComputedStyle(el1);
    const style2 = window.getComputedStyle(el2);
    const transform1 = style1.getPropertyValue("height");
    const transform2 = style2.getPropertyValue("height");
    el1.style.height = transform2;
    el2.style.height = transform1;
}


function bubbleSort() {
    let childElements =targetParent.children;
    console.log(childElements);
    for (let i = 0; i < numbers.length; i++) {
        for (let j = 0; j < numbers.length - i; j++)
        {
            childElements[j].style.backgroundColor = "red";
            childElements[j + 1].style.backgroundColor = "red";
            if (numbers[j] > numbers[j + 1]) {
                let temp=numbers[j];
                numbers[j]=numbers[j+1];
                numbers[j+1]=temp;
                swap(childElements[j], childElements[j + 1]);
            }
        }
        childElements[n - i].style.backgroundColor = "green";
    }
}

function createArray() {
    numbers.splice(0, numbers.length);
    targetParent.innerHTML = "";
    while (numbers.length < 100) {
        let r = Math.floor(Math.random() * 100);
        numbers.push(r);
    }
    console.log(numbers);

    let element = document.createElement("div");
    element.classList.add("bar");
    element.style.width = "10px";
    element.style.backgroundColor = "yellow";
    element.style.border = "1px solid";

    for (let i = 0; i < 100; i++) {
        element.style.height = `${numbers[i] * 3}px`;
        targetParent.appendChild(element.cloneNode(true));
    }
    let buttons = document.getElementsByClassName("sortbtn");
    Array.from(buttons).forEach((element) => {
        element.disabled = false;
    })
}

It creates random numbers from 1 to 100, creates respective div tags to represent the numbers and then sorts them using bubble sort. But I don't know why I am not getting the sorted result. It also shows the following error:

Uncaught TypeError: Cannot read properties of undefined (reading 'style')

This error occurs at this line:

 childElements[j].style.backgroundColor = "red";

But when I console.log(childElements), it successfully shows the created div tags to represent the numbers.

Please can someone help me out. Thanks in advance.