DialogJavaScript.html

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script>
  /**
   * Run initializations on dialog load.
   */
  $(function() {
    // Assign handler functions to dialog elements here, if needed.
    $('#alt-text-form').submit(onTextSave);

  });

  /**
   * Calls the server to modify the document.
   * Changes the document title to match the dialog text.
   */
  function onTextSave() {
    this.disabled = true;

    // Gather any information that needs to be sent to the server here.
    
    var altTexts = [];
    for (var i = 0; i < imageAlt.length; i++) {
      altTexts.push(document.getElementById('alt-text-' + i).value);
    }

    // Send the value to the server and handle the response.
    google.script.run
        .withSuccessHandler(
          function(msg, element) {
            // Respond to success conditions here.
            element.disabled = false;
          })
        .withFailureHandler(
          function(msg, element) {
            // Respond to failure conditions here.
            element.disabled = false;
          })
        .withUserObject(this)
        .setAltText(altTexts);
    return false;
  }


</script>