tauri-plugins-workspace/plugins/single-instance/examples/emit-event/public/index.html

<html>
  <body>
    <div>Plugin example</div>
    <pre id="args"></pre>
    <script type="module">
      var argsEl = document.getElementById('args')

      function cliProtocolVal({ args: { color: { value }}}) {
        argsEl.innerHTML = value
        document.body.style.backgroundColor = value
      }
      function cliProtocolErr (err) {
        argsEl.innerHTML = JSON.stringify(err)
      }

      window.__TAURI__.cli.getMatches()
        .then(cliProtocolVal)
        .catch(cliProtocolErr);

      await window.__TAURI__.event.listen(
        'single-instance',
        ({event, ...eventObj}) => {
          console.log(event, eventObj)
          let args = eventObj.payload?.args

          if (args?.length > 1) {
            let color = args[1]
            argsEl.innerHTML = color
            document.body.style.backgroundColor = color
          }
        }
      )
    </script>
  </body>
</html>