HTML5 Web Workers-unleashed

Editor's Notes

• #13: Google Chrome – every tab is its own program (not one tab within a program). So if one tab goes down, the whole app doesn't crash.
• #16: 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
• #26: The following steps are shown in the diagram: A user navigates to a location-aware application in the browser.The application web page loads and requests coordinates from the browser by making a Geolocation function call. The browser intercepts this and requests user permission. Let's assume that the permission is granted.The browser retrieves coordinate information from the device it is running on. For example, the IP address, Wi-Fi, or GPS coordinates. This is an internal function of the browser.The browser sends these coordinates to a trusted external location service, which returns a detailed location that can now be sent back to the host of the HTML5 Geolocation application.
• #39: The successCallback function parameter tells the browser which function you want called when the location data is made available. This is important because operations such as fetching location data may take a long time to complete. No user wants the browser to be locked up while the location is retrieved, and no developer wants his program to pause indefinitely—especially because fetching the location data will often be waiting on a user to grant permission. The successCallback is where you will receive the actual location information and act on it.However, as in most programming scenarios, it is good to plan for failure cases. It is quite possible that the request for location information may not complete for reasons beyond your control, and for those cases you will want to provide an errorCallback function that can present the user with an explanation, or perhaps make an attempt to try again. While optional, it is recommended that you provide one.Finally, an options object can be provided to the HTML5 Geolocation service to fine-tune the way it gathers data. This is an optional parameter that we will examine later.
• #41: The timeout value deals with the duration needed to calculate the location value, while maximumAge refers to the frequency of the location calculation. If any single calculation takes longer than the timeout value, an error is triggered. However, if the browser does not have an up-to-date location value that is younger than maximumAge, it must refetch another value. Special values apply here: setting the maximumAge to “0” requires the value to always be re-fetched, while setting it to Infinity means it should never be refetched.
• #44: This sample works by using the watchPosition() capability we discussed in the last section. Every time a new position is sent to us, we will compare it to the last known position and calculate the distance traveled. This is accomplished using a well-known calculation known as the Haversine formula, which allows us to calculate distance between two longitude and latitude positions on a sphere.
• #57: High-message volume, small message size scenario where long-polling is potentially worse than polling.
• #59: WebSocket is text-only
• #63: HTTP used for handshake onlyOperates over a single socketTraverses firewalls and routers seamlesslyAllows authorized cross-site communicationCookie-based authenticationExisting HTTP load balancersNavigates proxies using HTTP CONNECT, same technique as https, but without the encryption
• #64: Text type requires high-order bit setBinary type requires high-order bit _not_ setThere is no defined maximum size. However, the protocol allows either side (browser or server) to terminate the connection if it cannot receive a large frame. So far, the definition of too large is left up to the implementation.If the user agent is faced with content that is too large to behandled appropriately, then it must fail the Web Socket connection.There is probably a practical maximum, but we have not discovered it as far as I know.You can't have four gigabytes of data in JavaScript, so the practical max is <4GB for the JavaScript implementation.
• #69: 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
• #70: 150 ms (TCP round trip to set up the connection plus a packet for the message)50 ms (just the packet for the message)
• #74: Text type requires high-order bit setBinary type requires high-order bit _not_ setThere is no defined maximum size. However, the protocol allows either side (browser or server) to terminate the connection if it cannot receive a large frame. So far, the definition of too large is left up to the implementation.If the user agent is faced with content that is too large to behandled appropriately, then it must fail the Web Socket connection.There is probably a practical maximum, but we have not discovered it as far as I know.You can't have four gigabytes of data in JavaScript, so the practical max is <4GB for the JavaScript implementation.