Browser development tools
Firefox was the first browser to release a very complex debugger called Firebug which allowed developers to really understand what the front code was doing. All modern browsers now have pretty decent debuggers that can be added as an extension but Chrome’s developer tools seem to be the most widely used. Investing time in learning these tools will save you from pulling out all your hair.
Basics of SQL
If you are creating a web app, most likely your data will be stored in a database and your backend code will call that database to get what the user needs. The good news is you don’t have to be an expert in these databases anymore to use them because you will most likely use a package that will do all the heavy lifting but you will still need to understand the basics of how your data was stored.
Prior to the early 2000s when someone said “database” they meant a relational database. RDBMS (relational database management systems) store their data in structured tables with column names just like an Excel worksheet. In the last decade, a new type of unstructured database has emerged called NoSQL.