Evaluating page content to determine user interest

The disclosure is directed to approaches for combining server-side decisions based on user attributes and/or demographics with client-side decisions based on expressed or implied user interests determined based on the contents of a web page being visited by the user. A server is responsive to an occurrence of an operation of a client device at the web page. Processing steps determine particular executable web page content to send to the client device (e.g., where the particular executable web page content is determined in response to a particular client-side operation). The web page is rendered with the aforementioned executable web page content. Server-side processing receives messages that are emitted conditionally, based on the occurrence of a user event. An event log message comprises a portion of the web page, such as a string, indicating or implying user interest. A targeted advertisement is presented to the user based on the user interest.