For me, there was one project I worked on with my boss. The particular project had a super tight deadline but in the 8 weeks (with a few late nights with dinner at work), we smashed it all out meeting all of the client's requirements.
The project was a database controlled questionnaire where questions asked may changed depending on previous questions asked. Built in .NET, I remember writing some pretty crazy code to have dynamic validation (validation rules were in the DB) work in both the backend and the frontend. There were sections which were a one-to-many of more questions being answered too. There were upload fields, reports and an admin section. This site was built before React/Vue etc and used jQuery/ajax to communicate to the server. Due to the nature of the questions, the database had to be designed certain ways and due to client requirements, the whole site needed to support random spikes of high traffic.
The site had a few firsts for me like progressive use of JS on this scale: when available, the site would use it to do client side validation and nice animation between screens. Without it, the site would do full page submits.
It all worked perfectly and honestly, the client only had one or two issues with it for the years it had been up.
While I might implement it a bit differently now, I am quite proud of the build and the timeframe we built it in.
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