How to call a function in an html file from another html file

I'm trying to call a function from my html: tasks-div-upload.html to my other html: task-tareas-actualizadas.html.

I'm including my scripts on the script tags of the html files

I tried to call the function like this

First of all this is the html that calls the function: tasks-divs-upload.html

and the function is in task-tareas-actualizadas.html

I tried to call the function like i do in java that is

writing the class and then the function, for example: people.countPeople(5);

In this case, there are not classes because its an html file so what can I do?

//tasks-divs-upload.html

 function contadorTareas(){
   for(var x = 0; x < divs; x++){
     var numeroTareas = x;
   }
   prueba(numeroTareas);    // <---------
 } 

//task-tareas-actualizadas.html

function prueba(numero){
  console.log(numero);
}

Console shows this error "Uncaught ReferenceError: prueba is not defined"