The site alternativeto.net is dedicated to showing alternative software for all sorts of tasks. This includes tools in the greater area of software development. https://alternativeto.net/software/jsfiddle/
JSFiddle is one such tool for web develoment. As you can see there are others.
“jsFiddle lets one easily test snippets of JavaScript/CSS/HTML code on-the-fly”, the page says. Let us check it out at https://jsfiddle.net/.
The functionality of Codepen is quite similar to that of JSFiddle. The skin is different. Getting an account is free and easy. It may be used immediately. Look up https://codepen.io/.
If you have any doubts about what is offered at JS BIN, or what you are committing to if you sign in, go to https://jsbin.com/help/getting-started/ and see that it is quite quite non committal. The home is at https://jsbin.com/
With JS Bin there's a catch. You get an account only if you're on GitHub, and I am not. You are free to use it unregistered, but you cannot save your experiments. The site is run by Remy Sharp, co-author of Introduction to HTML5 where he writes the JavaScript parts. Check out [Law12].
