<body>
  <section class="heading">
    <div class="title">QRcodes</div>
    <div class="sub-title">Generate QRCode for anything!</div>
  </section>
  <section class="user-input">
    <label for="input_text">Type something...</label>
    <input type="text" name="input_text" id="input_text" autocomplete="off">
    <button class="button" type="submit">Generate QR Code</button>
  </section>
  <div class="qr-code" style="display: none;"></div>
</body>
:root {
  font-size: 62.5%;
}
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  text-size-adjust: none;
  -webkit-text-size-adjust: none;
}
button:hover {
  cursor: pointer;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  background-color: #eae6e5;
}
.heading {
  margin: 3rem 0 5rem 0;
}
.title,
.sub-title {
  font-size: 4rem;
  text-align: center;
  font-family: "Poppins", sans-serif;
  color: #12130f;
}
.sub-title {
  font-size: 1.5rem;
  color: #8f8073;
}

.user-input {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 100%;
}
.user-input label {
  text-align: center;
  font-size: 1.5rem;
  font-family: "Poppins", sans-serif;
}
.user-input input {
  width: 80%;
  max-width: 35rem;
  font-family: "Poppins", sans-serif;
  outline: none;
  border: none;
  border-radius: 0.5rem;
  background-color: #9b8774ad;
  text-align: center;
  padding: 0.7rem 1rem;
  margin: 1rem 1rem 2rem 1rem;
}
.button {
  outline: none;
  border: none;
  border-radius: 0.5rem;
  padding: 0.7rem 1rem;
  margin-bottom: 3rem;
  background-color: #5b92799d;
  color: #12130f;
  font-family: "Poppins", sans-serif;
}

.qr-code {
  border-top: 0.5rem solid #8f8073;
  border-right: 0.5rem solid #8f8073;
  border-bottom: 1rem solid #8f8073;
  border-radius: 0.5rem;
  border-bottom-left-radius: 0.5rem;
  border-bottom-right-radius: 0.5rem;
  border-left: 0.5rem solid #8f8073;
  background-color: #8f8073;
  margin-bottom: 6rem;
}
.qr-code button {
  display: flex;
  justify-content: center;
  background-color: #8f8073;
  font-family: "Poppins", sans-serif;
  color: #eae6e5;
  border: none;
  outline: none;
  width: 100%;
  height: 100%;
  margin-top: 1rem;
}
.qr-code button a {
  width: 100%;
  height: 100%;
  text-decoration: none;
  color: #eae6e5;
}
View Compiled
let btn = document.querySelector(".button");
let qr_code_element = document.querySelector(".qr-code");

btn.addEventListener("click", () => {
  let user_input = document.querySelector("#input_text");
  if (user_input.value != "") {
    if (qr_code_element.childElementCount == 0) {
      generate(user_input);
    } else {
      qr_code_element.innerHTML = "";
      generate(user_input);
    }
  } else {
    console.log("not valid input");
    qr_code_element.style = "display: none";
  }
});

function generate(user_input) {
  qr_code_element.style = "";

  var qrcode = new QRCode(qr_code_element, {
    text: `${user_input.value}`,
    width: 180, //128
    height: 180,
    colorDark: "#000000",
    colorLight: "#ffffff",
    correctLevel: QRCode.CorrectLevel.H
  });

  let download = document.createElement("button");
  qr_code_element.appendChild(download);

  let download_link = document.createElement("a");
  download_link.setAttribute("download", "qr_code.png");
  download_link.innerText = "Download";

  download.appendChild(download_link);

  let qr_code_img = document.querySelector(".qr-code img");
  let qr_code_canvas = document.querySelector("canvas");

  if (qr_code_img.getAttribute("src") == null) {
    setTimeout(() => {
      download_link.setAttribute("href", `${qr_code_canvas.toDataURL()}`);
    }, 300);
  } else {
    setTimeout(() => {
      download_link.setAttribute("href", `${qr_code_img.getAttribute("src")}`);
    }, 300);
  }
}

External CSS

  1. https://codepen.io/wolkanca/pen/wvgOPWb.css

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/qrcodejs/1.0.0/qrcode.min.js
  2. https://codepen.io/wolkanca/pen/wvgOPWb.js