1. The document discusses using Ajax to return JavaScript code and objects from a server. Code examples are provided to return a JavaScript function from a PHP file using XMLHttpRequest, and to convert text into a JavaScript object. 2. Methods for using the XMLHttpRequest HEAD method are demonstrated to retrieve header information from the server, such as the server name, date/time, and file modification date. 3. The code is modified to extract only the last modified date from the header, and then further modified to display individual parts of the date like date, month, year, hours, minutes, and seconds. 4. An example is given to check if a URL exists using HEAD requests and XMLHttpRequest.