Before I start let me just state that I am not a web developer and you might get better advice from others.
In my opinion C++ should be prefered when performance is required such as games. However for the web we need high level languages where we shouldn't have to worry about memory management. It's just must easier and faster. HTML, javascript and php are mainly used for web dev these days. They're not hard to pick up either.
WebAssembly, that chrome has just ditched for their own PNaCL can also be used to create nice looking, well performing games in the browser. http://webassembly.org/docs/c-and-c++/