This reads less like a "mistake", and more like just not giving any thought to what your code is doing as you write it. A mistake would be if the programmer mea

This reads less like a "mistake", and more like just not giving any thought to what your code is doing as you write it. A mistake would be if the programmer meant to implement X but instead implemented Y; this sounds more like the programmer just set out to implement Y without even considering other possibilities. Same for the framework change. An outdated framework might be a second or so slower, but a >30-second load time was never going to be fixed by updating. This is just bad problem-solving skills. When your app is taking 30 seconds to load, you don't just guess at what might make it faster -- you open your JS console and your log files, and you figure out where that time is being spent. Two minutes in the Performance tab of Chrome's developer tools, and you would have figured out the issue was on the back-end rather than the front-end.