Back in 2003 my fundamentals of CS course heavily relied on the interactions window of DrScheme (now DrRacket https://racket-lang.org/). It was a extremely powerful educational tool. When I started doing web development I found myself frequently putting snippets like `javascript:alert('abc'.substr(1)` into the URL bar. With the advent of the Firebug console it became even easier to try out new snippets. Now a days the Chrome console tab even has autocomplete. I'd be interested to know how these simple interactions contributed to the widespread adoption of JS and other languages.
Better completion usually makes me more productive no matter how crap the language is. Looking at you Java with your ginormous standard library with poor docs, and poor completion in eclipse.
