Day 9/90: Arrays — map, filter, reduce
90 Day JavaScript Challenge: Zero to Production
Today I wanted arrays to feel like a real engineering decision, not a syntax demo. The useful shift was making arrays — map, filter, reduce feel like clear values, collections, and function boundaries instead of syntax trivia.
The checks that mattered were collection shape and mutation rules, iteration or matching that keeps intent obvious, and defaults that do not hide missing data.
The failure mode I was actively trying to avoid was leaning on coercion or mutation until the value flow stops explaining itself. I wanted arrays to feel like something I could explain at a whiteboard or in a code review, not just something I recognized from docs.
That is the bar I want from this track: code that stays readable when requirements move, not just code that compiles today. I also want to keep tracing one concrete path through the code because that exposes weak assumptions faster than a larger demo.
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