Selection Sort Visualizer in JavaScript

Last Updated : 17 Oct, 2024

Selection sort is the simplest sorting algorithm that works by repeatedly finding the minimum element (considering ascending order) from the unsorted part and putting it at the beginning.

In order to know more about it. Please refer to Selection Sort

An algorithm like Selection Sort can be easily understood by visualizing instead of long codes. In this article, Selection Sort Visualizer is implemented using HTML, CSS & JavaScript.

Pre-requisites:

Selection Sort.
Basic HTML, CSS & JavaScript.
JavaScript promises.
JavaScript async/await function.

Approach

Button Generate New Array generates an array of random values usingthe Math.random() function and a bar corresponding to that value in terms of height.
Different colors are used to indicate which elements are unsorted(sky-blue), compared(darkblue & red) & sorted(lightgreen).
Button Selection Sort the elements using the selection sort algorithm.
Finally, elements are sorted.

Example: Click Generate New Array button to generate a new random array. Click the Selection Sort button to perform Visualization.

HTML

<!DOCTYPE html>
<html lang="en">

<!-- head -->

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" 
          content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />

    <!-- title -->
    <title>Sorting Visualizer</title>

    <!-- linking style.css -->
    <link href="style.css" rel="stylesheet" />
</head>

<!-- body -->

<body>
    <section class="head">Selection Sort Visualizer</section>
    <section class="data-container"></section>

    <!-- "Generate New Array" button -->
    <button class="btn1" onclick="generate()" id="Button1">
        Generate New Array</button>

    <!-- "Selection Sort" button -->
    <button class="btn2" 
            onclick="SelectionSort(),disable()" id="Button2">
        Selection Sort</button>
</body>

<!-- linking index.js -->
<script src="index.js"></script>

</html>

CSS

/* style.css */

.mySlides {
    display: none;
}

body {
    background-color: rgb(255, 235, 211);
    font-family: Verdana, sans-serif;
}

.head {
    margin-top: 20px;
    margin-right: 20vw;
    margin-left: 20vw;
    text-align: center;
    font-size: 30px;
    background-color: #6f459e;
    color: white;
    border-radius: 19px;
    font-weight: bolder;
}

.data-container {
    width: 600px;
    height: 384px;
    position: relative;
    margin: 0 auto;
}

.bar {
    width: 28px;
    position: absolute;
    left: 0;
    bottom: 0;
    background-color: rgb(0, 183, 255);
    transition: 0.2s all ease;
}

.bar__id {
    position: absolute;
    top: -24px;
    width: 100%;
    text-align: center;
}
.btn1 {
    padding: 12px;
    font-weight: bolder;
    background-color: #6f459e;
    border-radius: 10px;
    color: white;
    font-size: 16px;
    border: white;
    margin-left: 37vw;
    margin-top: 4vw;
    margin-right: 1vw;
}
.btn2 {
    padding: 12px;
    font-weight: bolder;
    background-color: #6f459e;
    border-radius: 10px;
    color: white;
    font-size: 16px;
    border: white;
}

JavaScript

// index.js

const container = document.querySelector(".data-container");

// function to generate bars
function generatebars(num = 20) {

    //for loop to generate 20 bars
    for (let i = 0; i < num; i += 1) {

        // To generate random values from 1 to 100
        const value = Math.floor(Math.random() * 100) + 1;

        // To create element "div"
        const bar = document.createElement("div");

        // To add class "bar" to "div"
        bar.classList.add("bar");

        // Provide height to the bar
        bar.style.height = `${value * 3}px`;

        // Translate the bar towards positive X axis 
        bar.style.transform = `translateX(${i * 30}px)`;

        // To create element "label"
        const barLabel = document.createElement("label");

        // To add class "bar_id" to "label"
        barLabel.classList.add("bar_id");

        // Assign value to "label"
        barLabel.innerHTML = value;

        // Append "Label" to "div"
        bar.appendChild(barLabel);

        // Append "div" to "data-container div"
        container.appendChild(bar);
    }
}

// asynchronous function to perform "Selection Sort"
async function SelectionSort(delay = 300) {
    let bars = document.querySelectorAll(".bar");
    // Assign 0 to min_idx
    let min_idx = 0;
    for (let i = 0; i < bars.length; i += 1) {

        // Assign i to min_idx
        min_idx = i;

        // Provide darkblue color to the ith bar
        bars[i].style.backgroundColor = "darkblue";
        for (let j = i + 1; j < bars.length; j += 1) {

            // Provide red color to the jth bar
            bars[j].style.backgroundColor = "red";

            // To pause the execution of code for 300 milliseconds
            await new Promise((resolve) =>
                setTimeout(() => {
                    resolve();
                }, 300)
            );

            // To store the integer value of jth bar to var1 
            let val1 = parseInt(bars[j].childNodes[0].innerHTML);

            // To store the integer value of (min_idx)th bar to var2 
            let val2 = parseInt(bars[min_idx].childNodes[0].innerHTML);

            // Compare val1 & val2
            if (val1 < val2) {
                if (min_idx !== i) {

                    // Provide skyblue color to the (min-idx)th bar
                    bars[min_idx].style.backgroundColor = "  rgb(24, 190, 255)";
                }
                min_idx = j;
            } else {

                // Provide skyblue color to the jth bar
                bars[j].style.backgroundColor = "  rgb(24, 190, 255)";
            }
        }

        // To swap ith and (min_idx)th bar
        let temp1 = bars[min_idx].style.height;
        let temp2 = bars[min_idx].childNodes[0].innerText;
        bars[min_idx].style.height = bars[i].style.height;
        bars[i].style.height = temp1;
        bars[min_idx].childNodes[0].innerText = bars[i].childNodes[0].innerText;
        bars[i].childNodes[0].innerText = temp2;

        // To pause the execution of code for 300 milliseconds
        await new Promise((resolve) =>
            setTimeout(() => {
                resolve();
            }, 300)
        );

        // Provide skyblue color to the (min-idx)th bar
        bars[min_idx].style.backgroundColor = "  rgb(24, 190, 255)";

        // Provide lightgreen color to the ith bar
        bars[i].style.backgroundColor = " rgb(49, 226, 13)";
    }

    // To enable the button "Generate New Array" after final(sorted)
    document.getElementById("Button1").disabled = false;
    document.getElementById("Button1").style.backgroundColor = "#6f459e";

    // To enable the button "Selection Sort" after final(sorted)
    document.getElementById("Button2").disabled = false;
    document.getElementById("Button2").style.backgroundColor = "#6f459e";
}

// Call "generatebars" function
generatebars();

// function to generate new random array 
function generate() {
    window.location.reload();
}

//  function to disable the button
function disable() {
    // To disable the button "Generate New Array"
    document.getElementById("Button1").disabled = true;
    document.getElementById("Button1").style.backgroundColor = "#d8b6ff";

    // To disable the button "Selection Sort"
    document.getElementById("Button2").disabled = true;
    document.getElementById("Button2").style.backgroundColor = "#d8b6ff";
}