Passing String Variable to a Function on Google App Script

I have text a variable with string type, I want to pass it to a function and change the value there just like previous post (using list type)

but, text variable value can't be changed by  passing to function like list (or array). I didn't have append or push syntax.

well, we can still use list

but list have comma, :(

so I updated the value by passing it to a function like this

function htmlOutput(form) {
  var text = 'Tadaa...';
  text+='Test'; 

text = dummy(text);
  return text;
}

function dummy(text){
text+='hehehe';
  return text;
}

.