Most web apps would require some sort of a back-end and storage. So you at least need to know some SQL and a server-side language (node.js is an option, but see

Most web apps would require some sort of a back-end and storage. So you at least need to know some SQL and a server-side language (node.js is an option, but seems much harder than PHP). And then you can't just "learn" javascript, you need to learn programming paradigms (data structures, control structures, how to modularize the code, etc).