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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <body onload="createCaptcha()">
  <form onsubmit="validateCaptcha()">
    <div id="captcha">
    </div>
    <input type="text" placeholder="Captcha" id="cpatchaTextBox"/>
    <button type="submit">Submit</button>
  </form>
</body>
!

CSS 

              
                input[type=text] {
    padding: 12px 20px;
    display: inline-block;
    border: 1px solid #ccc;
    border-radius: 4px;
    box-sizing: border-box;
}
button{
  background-color: #4CAF50;
    border: none;
    color: white;
    padding: 12px 30px;
    text-decoration: none;
    margin: 4px 2px;
    cursor: pointer;
}
canvas{
  /*prevent interaction with the canvas*/
  pointer-events:none;
}
!

JS 

              
                var code;
function createCaptcha() {
  //clear the contents of captcha div first 
  document.getElementById('captcha').innerHTML = "";
  var charsArray =
  "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ@!#$%^&*";
  var lengthOtp = 6;
  var captcha = [];
  for (var i = 0; i < lengthOtp; i++) {
    //below code will not allow Repetition of Characters
    var index = Math.floor(Math.random() * charsArray.length + 1); //get the next character from the array
    if (captcha.indexOf(charsArray[index]) == -1)
      captcha.push(charsArray[index]);
    else i--;
  }
  var canv = document.createElement("canvas");
  canv.id = "captcha";
  canv.width = 100;
  canv.height = 50;
  var ctx = canv.getContext("2d");
  ctx.font = "25px Georgia";
  ctx.strokeText(captcha.join(""), 0, 30);
  //storing captcha so that can validate you can save it somewhere else according to your specific requirements
  code = captcha.join("");
  document.getElementById("captcha").appendChild(canv); // adds the canvas to the body element
}
function validateCaptcha() {
  event.preventDefault();
  debugger
  if (document.getElementById("cpatchaTextBox").value == code) {
    alert("Valid Captcha")
  }else{
    alert("Invalid Captcha. try Again");
    createCaptcha();
  }
}
!
999px

Console