index.html

<html>
  <head>
    <title>Tiktok date extractor</title>
    <style>
      body {
        margin: 1em;
        font-family: "Helvetica", Arial, sans-serif;
        font-size: 18px;
      }
      button, input {
          font-size: 16px;
      }
      .form {
          margin-bottom: 1em;
      }
    </style>
  </head>
  <body>
    <script>
      function getVidId() {
        const tiktokUrl= document.querySelector("#url").value;
        // This regex should be safe as "Only letters, numbers, underscores, or periods are allowed" in TikTok usernames.
        const regex = /(?<=\/video\/)(.*?)(?=$|[^0-9])/;
        const vidId = regex.exec(tiktokUrl)[0];
        return vidId;
      }

      function extractUnixTimestamp(vidId) {
        // BigInt needed as we need to treat vidId as 64 bit decimal. This reduces browser support.
        const asBinary = BigInt(vidId).toString(2);
        const first31Chars = asBinary.slice(0, 31);
        const timestamp = parseInt(first31Chars, 2);
        return timestamp;
      }

      function unixTimestampToHumanDate(timestamp) {
        const milliseconds = timestamp * 1000;
        const dateObject = new Date(milliseconds);
        const humanDateFormat = dateObject.toUTCString()+" (UTC)";
        return humanDateFormat;
      }

      function getDate() {
        const vidId = getVidId();
        const unixTimestamp = extractUnixTimestamp(vidId);
        const humanDateFormat = unixTimestampToHumanDate(unixTimestamp);
        document.querySelector("#date").textContent = humanDateFormat;
      }
    </script>

    <div class="form">
      <label for="url">Tiktok video URL:</label>
      <input type="text" id="url" name="url" />
      <button onclick="getDate()">Get uploaded date</button>
    </div>
    <div class="output">
      <span id="label">Uploaded on: </span>
      <span id="date"></span>
    </div>
  </body>
</html>