Stack Exchange is using an old version of js-beautify to beautify JS, HTML, and CSS. Dynamic import isn't the only thing the old version gets wrong. It also breaks code when the code contains any of the following:

• Numeric separators (fixed in new version):

  1_000_000
  

  turns into

  1 _000_000
  

• Private fields (fixed in new version):

  class X { #foo = 'bar'; }
  

  turns into

  class X {#
    foo = 'bar';
  }
  

• Logical assignment (fixed in new version):

  a ||= b;
  

  turns into

  a || = b;
  

• Nullish coalescing (fixed in new version):

  x ?? y
  

  turns into

  x ? ? y
  

• Optional chaining (fixed in new version):

  x?.y?.z
  

  turns into

  x ? .y ? .z
  

The new version of js-beautify also supports dynamic import:

const code = `
await import('./module.js');   // GOOD

1_000_000                      // GOOD

class X { #foo = 'bar'; }      // GOOD

a ||= b;                       // GOOD

x ?? y                         // GOOD

x?.y?.z                        // GOOD
`;

console.log(js_beautify(code));

<script src="https://cdnjs.cloudflare.com/ajax/libs/js-beautify/1.14.6/beautify.min.js"></script>

Let's update js-beautify.

First, pick your favorite Javascript based Pretty Print/Beautifier. I prefer the one at http://jsbeautifier.org/, because it's what I found first. Downloads its file https://github.com/beautify-web/js-beautify/blob/master/js/lib/beautify.js

Second, download and install The Mozilla group's Java based Javascript engine, Rhino. "Install" is a little bit misleading; Download the zip file, extract everything, place js.jar in your Java classpath (or Library/Java/Extensions on OS X). You can then run scripts with an invocation similar to this

java -cp js.jar org.mozilla.javascript.tools.shell.Main name-of-script.js

Use the Pretty Print/Beautifier from step 1 to write a small shell script that will read in your javascript file and run it through the Pretty Print/Beautifier from step one. For example

//original code    
(function() { ... js_beautify code ... }());

//new code
print(global.js_beautify(readFile(arguments[0])));

Rhino gives javascript a few extra useful functions that don't necessarily make sense in a browser context, but do in a console context. The function print does what you'd expect, and prints out a string. The function readFile accepts a file path string as an argument and returns the contents of that file.

You'd invoke the above something like

java -cp js.jar org.mozilla.javascript.tools.shell.Main beautify.js file-to-pp.js

You can mix and match Java and Javascript in your Rhino run scripts, so if you know a little Java it shouldn't be too hard to get this running with text-streams as well.