GMail API Usage (doc needed)

gapi-mail.js

// Client ID and API key from the Developer Console
var CLIENT_ID = '668438714568-cd8dit8kvrd14tqdl49e3hlmlnlgmdn7.apps.googleusercontent.com';
var API_KEY = 'AIzaSyCL2XxiaMpu6D3z5MqxBLO2cOvdIyDAhiE';

// Array of API discovery doc URLs for APIs used by the quickstart
var DISCOVERY_DOCS = ["https://www.googleapis.com/discovery/v1/apis/gmail/v1/rest"];

// Authorization scopes required by the API; multiple scopes can be
// included, separated by spaces.
var SCOPES = 'https://www.googleapis.com/auth/gmail.readonly';

var authorizeButton = document.getElementById('authorize_button');
var signoutButton = document.getElementById('signout_button');

/**
 *  On load, called to load the auth2 library and API client library.
 */
function handleClientLoad() {
  gapi.load('client:auth2', initClient);
}

/**
 *  Initializes the API client library and sets up sign-in state
 *  listeners.
 */
function initClient() {
  gapi.client.init({
    apiKey: API_KEY,
    clientId: CLIENT_ID,
    discoveryDocs: DISCOVERY_DOCS,
    scope: SCOPES
  }).then(function () {
    // Listen for sign-in state changes.
    gapi.auth2.getAuthInstance().isSignedIn.listen(updateSigninStatus);

    // Handle the initial sign-in state.
    updateSigninStatus(gapi.auth2.getAuthInstance().isSignedIn.get());
    authorizeButton.onclick = handleAuthClick;
    signoutButton.onclick = handleSignoutClick;
  }, function(error) {
    appendPre(JSON.stringify(error, null, 2));
  });
}

/**
 *  Called when the signed in status changes, to update the UI
 *  appropriately. After a sign-in, the API is called.
 */
function updateSigninStatus(isSignedIn) {
  if (isSignedIn) {
    authorizeButton.style.display = 'none';
    signoutButton.style.display = 'block';
    listLabels();
  } else {
    authorizeButton.style.display = 'block';
    signoutButton.style.display = 'none';
  }
}

/**
 *  Sign in the user upon button click.
 */
function handleAuthClick(event) {
  gapi.auth2.getAuthInstance().signIn();
}

/**
 *  Sign out the user upon button click.
 */
function handleSignoutClick(event) {
  gapi.auth2.getAuthInstance().signOut();
}

/**
 * Append a pre element to the body containing the given message
 * as its text node. Used to display the results of the API call.
 *
 * @param {string} message Text to be placed in pre element.
 */
function appendPre(message) {
  var pre = document.getElementById('content');
  var textContent = document.createTextNode(message + '\n');
  pre.appendChild(textContent);
}

/**
 * Print all Labels in the authorized user's inbox. If no labels
 * are found an appropriate message is printed.
 */
function listLabels() {
  gapi.client.gmail.users.labels.list({
    'userId': 'me'
  }).then(function(response) {
    var labels = response.result.labels;
    appendPre('Labels:');

    if (labels && labels.length > 0) {
      for (i = 0; i < labels.length; i++) {
        var label = labels[i];
        appendPre(label.name)
      }
    } else {
      appendPre('No Labels found.');
    }
  });
}

/**
* Retrieve Messages in user's mailbox matching query.
*
* @param  {String} userId User's email address. The special value 'me'
* can be used to indicate the authenticated user.
* @param  {String} query String used to filter the Messages listed.
* @param  {Function} callback Function to call when the request is complete.
*/
function listMessages(userId, query) {
var getPageOfMessages = function(request, result) {
request.execute(function(resp) {
// console.log(resp.messages.id);
// console.log(resp.messages.length);
var table = document.getElementById('emails');
table.innerHTML= '<tr><th>From</th><th>To</th><th>Content</th></tr>';
for (var i=0; i<resp.messages.length; i++){
    var request = gapi.client.gmail.users.messages.get({
        'userId': userId,
        'id': resp.messages[i].id
      }).then(function(response){
          table.innerHTML=table.innerHTML+ "<tr><td>" + response.result.payload.headers[22].value + "</td><td>" + response.result.payload.headers[23].value + "</td><td>" + response.result.snippet +"</td></tr>";
      });
}
result = result.concat(resp.messages);
// console.log(result);
var nextPageToken = resp.nextPageToken;
if (nextPageToken) {
  request = gapi.client.gmail.users.messages.list({
    'userId': userId,
    'pageToken': nextPageToken,
    'q': query
  });
  getPageOfMessages(request, result);
} else {
  console.log("esle");
}
});
};
var initialRequest = gapi.client.gmail.users.messages.list({
'userId': userId,
'q': query
});
getPageOfMessages(initialRequest, []);
}
/**
 * Get Message with given ID.
 *
 * @param  {String} userId User's email address. The special value 'me'
 * can be used to indicate the authenticated user.
 * @param  {String} messageId ID of Message to get.
 * @param  {Function} callback Function to call when the request is complete.
 */
function getMessage(userId, messageId) {
    var request = gapi.client.gmail.users.messages.get({
      'userId': userId,
      'id': messageId
    }).then(function(response){
        console.log(response.result.payload.headers[22].value);
        console.log(response.result.snippet);
        console.log(response.result.payload.headers[23].value)
    });
  }