Custom Captcha Security in JavaScript

This code implements a custom Captcha security system in JavaScript. It generates a grid of random numbers and marks a subset of them for the user to identify. This Captcha helps verify user interactions on websites.

You can use this code on your website’s forms to enhance security. It helps prevent automated bots from submitting forms by requiring users to solve the Captcha puzzle. This improves your website’s security and ensures that real users are interacting with your content.

How to Create Custom Captcha Security in JavaScript

1. Start by creating an HTML form on your webpage where you want to implement the Captcha. You can copy and paste the following HTML code. This code includes the form, Captcha container, and input field.

<form action="#" method="POST" class="main-form" id="mainForm">
    <h1 id="resultCapcha"></h1>  
    <svg class="patternDrow" height="250" width="250" id="patternDrowPolyline"></svg>  
    <div class="captcha-container" id="captchaContainer">
      <!-- Captcha Items go here -->
      
    </div>
    <div class="input-group">
      <label for="captchaInput">Insert the marked numbers in order <br/> (starting from top left)</label>
      <input type="text" autocomplete="off" id="captchaInput">
    </div>
    <input type="submit" value="Submit" class="btn submit-btn">
  </form>

2. The CSS code included in the snippet ensures that your Captcha looks visually appealing and fits well with your website’s design. Feel free to customize the styles to match your site’s theme.

@import url('https://fonts.googleapis.com/css2?family=Rubik:wght@400;500;600&display=swap');

*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Rubik', sans-serif;
}

html {
  font-size: 10px;
}

body {
  width: 100%;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.captcha-wrong
{
color: red;
}
.captcha-success
{
color: rgb(5, 201, 15);
}
.marked{
  background-color: royalblue !important;
}
.patternDrow{
  position: absolute;
  z-index: 100;  
  margin-left: 5%;
  text-align: center;
}
.main-form {
  background: #fff;
  width: 40rem;
  padding: 3rem 2rem;
  box-shadow: 0 0 1rem .1rem rgba(0, 0, 0, 0.1);
  border-radius: .5rem;
}

.captcha-container {
  display: grid;
  justify-content: center;
  grid-template-columns: repeat(3, 8rem);
  grid-auto-rows: 8rem;
  grid-gap: .5rem;
  margin-bottom: 2rem;
}

.captcha-item {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: rgb(237, 237, 237);
  font-size: 3rem;
  font-weight: 500;
  position: relative;
}

.marked::before {
  content: "✔";
  position: absolute;
  top: .5rem;
  right: .5rem;
  font-size: 2rem;
}

label[for="captchaInput"] {
  font-size: 1.6rem;
  font-weight: 500;
}

#captchaInput {
  display: block;
  width: 100%;
  padding: .8rem 1rem;
  margin-top: 1rem;
  border: .1rem solid rgba(0, 0, 0, .3);
  border-radius: .5rem;
   box-sizing: border-box;
}

.submit-btn {
  margin-top: 2rem;
  padding: .8rem 2rem;
  color: white;
  background-color: black;
  border: none;
  border-radius: .5rem;
  outline: none;
  font-size: 1.6rem;
  cursor: pointer;
}

.submit-btn:hover {
  background-color: rgba(0, 0, 0, 0.8);
}

3. Finally, add the following JavaScript code to your project. This code generates a dynamic Captcha with random numbers and highlights specific numbers for user identification. It also verifies user input against the generated Captcha.

const captchaContainer = document.querySelector("#captchaContainer");
const captchaInput = document.querySelector("#captchaInput");
const mainForm = document.querySelector("#mainForm");
const resultCapcha = document.querySelector("#resultCapcha");
const patternDrowPolyline = document.querySelector("#patternDrowPolyline");
const gridCount = 9;

let result = "";

const createCaptcha = () => {
  var points = "";
  var markCount = 0;
  var captchaItemList = []; 

  for (let i = 0; i < gridCount; i++) {
    var captchaItem = document.createElement("div");
    captchaItem.classList.add("captcha-item");
    // captchaItem.id = `captcha-item-${i}`;

    const randNum = Math.random().toString(20).substr(2, 1);
    
    captchaContainer.appendChild(captchaItem);
    captchaItem.innerHTML = randNum;
  }
    
  const captchaItemId = document.getElementsByClassName("captcha-item");


    while(markCount < 5){
        let selectCaptchaItem = Math.floor(Math.random() * 8);
        
        if(captchaItemList.includes(selectCaptchaItem) == false){
            captchaItemList.push(selectCaptchaItem);
            captchaItemId[selectCaptchaItem].classList.add("marked");
            markCount++;
        }
    }

    captchaItemList.sort();

    captchaItemList.forEach(element => {
        switch (element) {
            case 0:
            points += "40,40,";
            break;
            case 1:
            points += "125,40,";
            break;
            case 2:
            points += "210,40,";
            break;
            case 3:
            points += "40,120,";
            break;
            case 4:
            points += "125,120,";
            break;
            case 5:
            points += "210,120,";
            break;
            case 6:
            points += "40,210,";
            break;
            case 7:
            points += "125,210,";
            break;
            case 8:
            points += "210,210,";
            break;
        }

        result += captchaItemId[element].innerHTML;    
    });
    patternDrowPolyline.innerHTML = ("<polyline points='" + points + "' style='fill:none;stroke:rgb(38, 216, 2);stroke-width:3' />");
    console.log(captchaItemList);
      

    // }
  // alert(points);
//   patternDrowPolyline.innerHTML = ("<polyline points='" + points + "' style='fill:none;stroke:rgb(38, 216, 2);stroke-width:3' />");
};

createCaptcha();

captchaInput.addEventListener("input", () => {
  // alert('val'+captchaInput.value );
  // alert('res'+result );
  if (captchaInput.value != result) {
    captchaInput.classList.add("wrong-captcha");
    resultCapcha.innerHTML = "Wrong Captcha";
    resultCapcha.classList.add("captcha-wrong");
    resultCapcha.classList.remove("captcha-success");
  } else {
    captchaInput.classList.remove("wrong-captcha");
    resultCapcha.classList.remove("captcha-wrong");
    resultCapcha.classList.add("captcha-success");
    resultCapcha.innerHTML = "Captcha Verified";
  }
});

// Get the modal
var modal = document.getElementById("myModal");
// Get the button that opens the modal
var btn = document.getElementById("submit");
// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];
var message = document.getElementById("message");

btn.onclick = function() {
  if (captchaInput.value != result) {
    modal.style.display = "block";
    message.innerHTML = "Wrong Captcha!! Try again"
    message.style.color = "red";
  } else {
    modal.style.display = "block";
    message.innerHTML = "Captcha Varified"
    message.style.color = "green";
  }
}

span.onclick = function() {
  modal.style.display = "none";
}

// mainForm.addEventListener("submit", (e) => {
//   if (
//     captchaInput.classList.contains("wrong-captcha") ||
//     (!captchaInput.value.length && result.length)
//   ) {
//     e.preventDefault();
//   }
// });

That’s all! hopefully, you have successfully created a custom Captcha Security in JavaScript. If you have any questions or suggestions, feel free to comment below.

Asif Mughal

I code and create web elements for amazing people around the world. I like work with new people. New people new Experiences.
I truly enjoy what I’m doing, which makes me more passionate about web development and coding. I am always ready to do challenging tasks whether it is about creating a custom CMS from scratch or customizing an existing system.