Worse, imagine if someone set their shell as the suffix alias for .sh, just to save time on their curl shell pipes... Oh the horror. Suffix aliases should come with a big caveat.
Really? Last time I downloaded a .js file by accident was never if my memory doesn't fail me (.html I remember a couple). Even if I did, I normally use the UI to manage my files. The only time I might try to do something with the CLI and a JS file is exactly to run `node file.js`, and this is just a convenience.
I can see opening up in an editor as useful shortcut. But actually executing code without an executable bit seems a bit more dangerous.