@sonam_murarkar a long long time ago, when console.log() was not yet invented, the primitive javascript developers use document.write() to debug their code, and alert() sometimes.
@josecalderon I once sat next to Dijkstra at dinner. I asked him why he didn't use category theory, as it's the ultimate theory of programming? His response was: "If I was as young as you, this is what I would do. But I'm too old now, so it's up to your generation". This was 30+ years ago.