I was thinking of including with

    <script src="mod.js"> </script>

just how you include (or included in the past) jquery or mathjax. I manage my namespaces like

    function Zebras() {

      let l;  //local
      let e;  //has setter and getter
 
      gete =  () => {return e}
      sete = (x) => {e = x}

      function lfunc() {console.log("local function")}
      function efunc() {console.log("exported function")}
 
      // exports :
      this.efunc = efunc
      this.gete  = gete
      this.sete  = sete
   }

and import it

    <script src="mod.js"> </script>

    <script> 
 
      zr = new Zebras()

      zr.sete(4)
      console.log( zr.gete() ) // 4

      zr.efunc()
      // zr.lfunc() <- not working
 
    </script>

You can export objects or functions trivially. I don't think you can expose primitives this way.

I think this method is working since ~20 years, and will work 20 years from now, when you can't even get your bundlers to run. But then if you have to change it frequently, probably ES modules are easier to automate, test, and handle with bundlers.