Channel API Javascript Reference (Java)

Use the following reference when building JavaScript clients for the channel API.

Building your JavaScript client

Include the following in your html page before any JavaScript code that refers to it:

<script type="text/javascript" src="/_ah/channel/jsapi"></script>

All other JavaScript code must be between the <body> tags of the page. For best performance, place your JavaScript code at the bottom of your HTML markup just before the </body>.

goog.appengine.Channel() Class


Create a channel object using the token returned by the createChannel() call on the server.



Open a socket on this channel. open() returns a goog.appengine.Socket object. You can set the callback properties directly on the returned socket object or set them using an optional object handler with the following properties:

  • onopen
  • onmessage
  • onerror
  • onclose

If the token specified during channel creation is invalid or expired then the onerror and onclose callbacks will be called. The code field for the error object will be 401 (Unauthorized) and the description field will be 'Invalid+token.' or 'Token+timed+out.' respectively. The onerror callback is also called asynchronously whenever the token for the channel expires. An onerror call is always followed by an onclose call and the channel object will have to be recreated after this event.

goog.appengine.Socket() Class


Close the socket. The socket cannot be used again after calling close; the server must create a new socket.


Set this to a function called when the socket is ready to receive messages.
Set this to a function called when the socket receives a message. The function is passed one parameter: a message object. The data field of this object is the string passed to the send_message method on the server.
Set this property to a function called when an error occurs on the socket. The function is passed one parameter: an error object. The description field is a description of the error and the code field is an HTTP error code indicating the error.
Set this property to a function that called when the socket is closed. When the socket is closed, it cannot be reopened. Use the open() method on a goog.appengine.Channel object to create a new socket.

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App Engine standard environment for Java