The FileReaderSync interface allows to read File or Blob objects in a synchronous way.
If you would like to use the WebSocket API, it is useful if you have a server. In this article I will show you how to write one in C#. You can do it in any server-side language, but to keep things simple and more understandable, I chose Microsoft's language.
Microformats (sometimes abbreviated μF) are simple conventions used to embed semantics in HTML and quickly provide an API to be used by search engines, aggregators, and other tools. These small patterns of HTML are used for marking entities that range from fundamental to domain-specific information, such as people, organizations, events, and locations. 
The beforeunload event is fired when the window, the document and its resources are about to be unloaded.
Page transition events fire when a webpage is being loaded or unloaded.
This example shows you how to create a WebSocket API server using Oracle Java.

Although other server-side languages can be used to create a WebSocker server, this example uses Oracle Java to simplify the example code.
A Boolean value indicating whether or not the device's battery is currently being charged.
Indicates the amount of time, in seconds, that remain until the battery is fully charged.
Indicates the amount of time, in seconds, that remains until the battery is fully discharged.
Indicates the current battery charge level as a value between 0.0 and 1.0.
parentStyleSheet returns the stylesheet object in which the current rule is defined.
The elementFromPoint() method of the Document interface returns the topmost element at the specified coordinates.
Returns an HTMLCollection object containing one or more HTMLEmbedElements or null which represent the <embed> elements in the current document.
This method is called whenever an event occurs of the type for which the EventListener interface was registered.
The onblur property returns the onBlur event handler code, if any, that exists on the current element.
The onkeypress property sets and returns the onKeyPress event handler code for the current element.
The hashchange event is fired when the fragment identifier of the URL has changed (the part of the URL that follows the # symbol, including the # symbol).