Easily getting variable values from WebGL in Browser

I'm developing some 3D interactions in Unity, and they will be embedded in a webpage which will have other interactive components. I'm going to need to communicate between these other components, and I'm wondering if there's an easy way to return a value from Unity into JS variables in the browser.

I know I can use SendMessage() to call functions in Unity from external JS, but can I return values from these calls?

I don't know how to efficiently do this, so the solution I'm thinking of right now looks like this:

Browser:

    var health;
    var exp;
         
         function GetHealth(){
             SendMessage("Player", "GetHealth");
         }
         
         function ReturnValue(varName, val){
            if(varName == "health"){
               health = val;
            }
     
        if(varName == "exp"){
               exp = val;
            }
 
         //etc.

         }

Unity:

 public void GetHealth(){
     Application.ExternalCall("ReturnValue", "health", health); 
 }

This is a really ugly solution that would be ripe with problems. Ideally, I'd like to do something like

Browser:

 function GetHealth(){
    return SendMessage("Player", "GetHealth");
 }

Unity:

 public int GetHealth(){
    return health;
 }

Any ideas?