Basics: How do I get these 2 scripts to communicate?

[joda]

//main script

var action = "stop";

function update(){

   otherScript.update(whatDoIWriteHere);

}
update();

//other script

export class OtherScript {
  
  update(mainScript) {
    mainScript.action = "go";
  }

}

I'd like to set up my code to work this way, mainly to keep my code cleaner. Note the "whatDoIWritehere" above. I've tried to google around and get a simple answer, but it's pretty tricky. Any help here? Thank you!

Edited March 26, 2020 by joda