For JavaScript, the answer is pretty obvious: there simply weren't (and still aren't, really) any alternatives. For Python, it's really a phenomenon of trends.

For JavaScript, the answer is pretty obvious: there simply weren't (and still aren't, really) any alternatives. For Python, it's really a phenomenon of trends. It's got all the right pieces (easy to learn and use, good community, good library ecosystem), but lots of languages have that. Like so many other things... It became more popular because it was popular. Runtime performance is only one factor in the programming language game. Many other equally important factors are purely emotional. We are human, after all.