Exception Handling | Web SDK

A best practice when programming is to write code that assumes and anticipates that things will go wrong. For example, a client may not be connected to the internet when trying to connect to a session.

The Web SDK includes completion handlers and exception events that reveal exceptions at run time.

Completion handlers

For many methods that complete asynchronously, the final parameter you pass in is a completion handler function. This function is called when the method completes or fails. If it fails, the function is passed an error object as a parameter.

For example, the following code calls the Session.connect() method, passing in a completion handler:

var session = OT.initSession(apiKey, session);
session.connect(token, function (error) {
    if (error) {
    console.log("Failed to connect: ", error.message);
    if (error.name === "OT_NOT_CONNECTED") {
        alert("You are not connected to the internet. Check your network connection.");
    }
    } else {
    console.log("Connected");
    }
});

It is important to implement completion handlers to see when a method succeeds or fails. In some cases, you can prompt the user if there is a client condition that caused the error. For example, if the error.name property is set to "OT_NOT_CONNECTED" when calling the Session.connect() method fails, this indicates that the client is not connected to the network.

For other error conditions that are not the fault of the client, you can examine the error code and message to see the nature of the error. For example, when calling the Session.connect() method fails, an error code of 1004 indicates that you tried to connect with an invalid token. This could be a token that is expired or that does not match the session you are connecting to. Check the message property of the error object for details.

Methods with completion handlers

The following methods in the Web SDK include a completionHandler parameter. For this optional parameter, you can pass in a function that is called when the method succeeds or fails:

• Session.forceDisconnect()
• Session.forceUnpublish()
• Session.connect()
• Session.publish()
• Session.signal()
• Session.subscribe()
• OT.initPublisher()

Check the message property for more details about the error.

In the event of an error, the code value of the error parameter can have one of the following values:

Listening for exception events

To detect all exception events, add an event listener for the exception event, dispatched by the OT object. However, it is easier to react to errors in completion handlers for specific methods.