Send Email & View Inbox Messages Using JavaScript Gmail API

In this tutorial, you will learn how to send an email and view inbox messages using JavaScript Gmail API. I have provided the complete source code of Gmail API JavaScript example below.
Project Screenshots

Here are some screenshots of Gmail API JavaScript example app that we will be creating today.
View Inbox Messages Using JavaScript Gmail API
Gmail API JavaScript Example

index.html

Important Note:
On line # 109, replace ### YOUR CLIENT ID ### with your actual OAuth client ID that you got from Google Developer Console.
On line # 110, replace ### YOUR API KEY ### with your actual API key that you got from Google Developer Console.
Google Developer Console API key and OAuth client ID
<!doctype html>
<html>
  <head>
    <title>Gmail API demo</title>
    <meta charset="UTF-8">

    <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
    <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">
    <style>
      iframe {
        width: 100%;
        border: 0;
        min-height: 80%;
        height: 600px;
        display: flex;
      }
    </style>
  </head>
  <body>
    <div class="container">
      <h1>Gmail API demo</h1>

      <a href="#compose-modal" data-toggle="modal" id="compose-button" class="btn btn-primary pull-right hidden">Compose</a>

      <button id="authorize-button" class="btn btn-primary hidden">Authorize</button>

      <table class="table table-striped table-inbox hidden">
        <thead>
          <tr>
            <th>From</th>
            <th>Subject</th>
            <th>Date/Time</th>
          </tr>
        </thead>
        <tbody></tbody>
      </table>
    </div>

    <div class="modal fade" id="compose-modal" tabindex="-1" role="dialog">
      <div class="modal-dialog modal-lg">
        <div class="modal-content">
          <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal" aria-label="Close">
              <span aria-hidden="true">×</span>
            </button>
            <h4 class="modal-title">Compose</h4>
          </div>
          <form onsubmit="return sendEmail();">
            <div class="modal-body">
              <div class="form-group">
                <input type="email" class="form-control" id="compose-to" placeholder="To" required />
              </div>

              <div class="form-group">
                <input type="text" class="form-control" id="compose-subject" placeholder="Subject" required />
              </div>

              <div class="form-group">
                <textarea class="form-control" id="compose-message" placeholder="Message" rows="10" required></textarea>
              </div>
            </div>
            <div class="modal-footer">
              <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
              <button type="submit" id="send-button" class="btn btn-primary">Send</button>
            </div>
          </form>
        </div>
      </div>
    </div>

    <div class="modal fade" id="reply-modal" tabindex="-1" role="dialog">
      <div class="modal-dialog modal-lg">
        <div class="modal-content">
          <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal" aria-label="Close">
              <span aria-hidden="true">×</span>
            </button>
            <h4 class="modal-title">Reply</h4>
          </div>
          <form onsubmit="return sendReply();">
            <input type="hidden" id="reply-message-id" />

            <div class="modal-body">
              <div class="form-group">
                <input type="text" class="form-control" id="reply-to" disabled />
              </div>

              <div class="form-group">
                <input type="text" class="form-control disabled" id="reply-subject" disabled />
              </div>

              <div class="form-group">
                <textarea class="form-control" id="reply-message" placeholder="Message" rows="10" required></textarea>
              </div>
            </div>
            <div class="modal-footer">
              <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
              <button type="submit" id="reply-button" class="btn btn-primary">Send</button>
            </div>
          </form>
        </div>
      </div>
    </div>

    <script src="//code.jquery.com/jquery-1.11.3.min.js"></script>
    <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

    <script type="text/javascript">
      var clientId = '### YOUR CLIENT ID ###'
      var apiKey = '### YOUR API KEY ###';
      var scopes =
        'https://www.googleapis.com/auth/gmail.readonly '+
        'https://www.googleapis.com/auth/gmail.send';

      function handleClientLoad() {
        gapi.client.setApiKey(apiKey);
        window.setTimeout(checkAuth, 1);
      }

      function checkAuth() {
        gapi.auth.authorize({
          client_id: clientId,
          scope: scopes,
          immediate: true
        }, handleAuthResult);
      }

      function handleAuthClick() {
        gapi.auth.authorize({
          client_id: clientId,
          scope: scopes,
          immediate: false
        }, handleAuthResult);
        return false;
      }

      function handleAuthResult(authResult) {
        if(authResult && !authResult.error) {
          loadGmailApi();
          $('#authorize-button').remove();
          $('.table-inbox').removeClass("hidden");
          $('#compose-button').removeClass("hidden");
        } else {
          $('#authorize-button').removeClass("hidden");
          $('#authorize-button').on('click', function(){
            handleAuthClick();
          });
        }
      }

      function loadGmailApi() {
        gapi.client.load('gmail', 'v1', displayInbox);
      }

      function displayInbox() {
        var request = gapi.client.gmail.users.messages.list({
          'userId': 'me',
          'labelIds': 'INBOX',
          'maxResults': 10
        });
        request.execute(function(response) {
          $.each(response.messages, function() {
            var messageRequest = gapi.client.gmail.users.messages.get({
              'userId': 'me',
              'id': this.id
            });
            messageRequest.execute(appendMessageRow);
          });
        });
      }

      function appendMessageRow(message) {
        $('.table-inbox tbody').append(
          '<tr>\
            <td>'+getHeader(message.payload.headers, 'From')+'</td>\
            <td>\
              <a href="#message-modal-' + message.id +
                '" data-toggle="modal" id="message-link-' + message.id+'">' +
                getHeader(message.payload.headers, 'Subject') +
              '</a>\
            </td>\
            <td>'+getHeader(message.payload.headers, 'Date')+'</td>\
          </tr>'
        );
        var reply_to = (getHeader(message.payload.headers, 'Reply-to') !== '' ?
          getHeader(message.payload.headers, 'Reply-to') :
          getHeader(message.payload.headers, 'From')).replace(/\"/g, '"');

        var reply_subject = 'Re: '+getHeader(message.payload.headers, 'Subject').replace(/\"/g, '"');
        $('body').append(
          '<div class="modal fade" id="message-modal-' + message.id +
              '" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">\
            <div class="modal-dialog modal-lg">\
              <div class="modal-content">\
                <div class="modal-header">\
                  <button type="button"\
                          class="close"\
                          data-dismiss="modal"\
                          aria-label="Close">\
                    <span aria-hidden="true">×</span></button>\
                  <h4 class="modal-title" id="myModalLabel">' +
                    getHeader(message.payload.headers, 'Subject') +
                  '</h4>\
                </div>\
                <div class="modal-body">\
                  <iframe id="message-iframe-'+message.id+'" srcdoc="<p>Loading...</p>">\
                  </iframe>\
                </div>\
                <div class="modal-footer">\
                  <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>\
                  <button type="button" class="btn btn-primary reply-button" data-dismiss="modal" data-toggle="modal" data-target="#reply-modal"\
                  onclick="fillInReply(\
                    \''+reply_to+'\', \
                    \''+reply_subject+'\', \
                    \''+getHeader(message.payload.headers, 'Message-ID')+'\'\
                    );"\
                  >Reply</button>\
                </div>\
              </div>\
            </div>\
          </div>'
        );
        $('#message-link-'+message.id).on('click', function(){
          var ifrm = $('#message-iframe-'+message.id)[0].contentWindow.document;
          $('body', ifrm).html(getBody(message.payload));
        });
      }

      function sendEmail()
      {
        $('#send-button').addClass('disabled');

        sendMessage(
          {
            'To': $('#compose-to').val(),
            'Subject': $('#compose-subject').val()
          },
          $('#compose-message').val(),
          composeTidy
        );

        return false;
      }

      function composeTidy()
      {
        $('#compose-modal').modal('hide');

        $('#compose-to').val('');
        $('#compose-subject').val('');
        $('#compose-message').val('');

        $('#send-button').removeClass('disabled');
      }

      function sendReply()
      {
        $('#reply-button').addClass('disabled');

        sendMessage(
          {
            'To': $('#reply-to').val(),
            'Subject': $('#reply-subject').val(),
            'In-Reply-To': $('#reply-message-id').val()
          },
          $('#reply-message').val(),
          replyTidy
        );

        return false;
      }

      function replyTidy()
      {
        $('#reply-modal').modal('hide');

        $('#reply-message').val('');

        $('#reply-button').removeClass('disabled');
      }

      function fillInReply(to, subject, message_id)
      {
        $('#reply-to').val(to);
        $('#reply-subject').val(subject);
        $('#reply-message-id').val(message_id);
      }

      function sendMessage(headers_obj, message, callback)
      {
        var email = '';

        for(var header in headers_obj)
          email += header += ": "+headers_obj[header]+"\r\n";

        email += "\r\n" + message;

        var sendRequest = gapi.client.gmail.users.messages.send({
          'userId': 'me',
          'resource': {
            'raw': window.btoa(email).replace(/\+/g, '-').replace(/\//g, '_')
          }
        });

        return sendRequest.execute(callback);
      }

      function getHeader(headers, index) {
        var header = '';
        $.each(headers, function(){
          if(this.name.toLowerCase() === index.toLowerCase()){
            header = this.value;
          }
        });
        return header;
      }

      function getBody(message) {
        var encodedBody = '';
        if(typeof message.parts === 'undefined')
        {
          encodedBody = message.body.data;
        }
        else
        {
          encodedBody = getHTMLPart(message.parts);
        }
        encodedBody = encodedBody.replace(/-/g, '+').replace(/_/g, '/').replace(/\s/g, '');
        return decodeURIComponent(escape(window.atob(encodedBody)));
      }

      function getHTMLPart(arr) {
        for(var x = 0; x <= arr.length; x++)
        {
          if(typeof arr[x].parts === 'undefined')
          {
            if(arr[x].mimeType === 'text/html')
            {
              return arr[x].body.data;
            }
          }
          else
          {
            return getHTMLPart(arr[x].parts);
          }
        }
        return '';
      }
    </script>
    <script src="https://apis.google.com/js/client.js?onload=handleClientLoad"></script>
  </body>
</html>
Project Screenshots

Gmail API JavaScript Example

index.html

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