How to change value of an object with a Javasciprt Funtion?

I understand that previous questions have concluded that JS is a pass-by-value language and onject falues can not be modified by using a function to declare their new value. However, I would like to see how COULD it be possible. For example I have the following code:

var oneBoolean = true;
var oneInput = undefined;

if (oneInput === undefined){
   oneBoolean = false;
}

I understand that this doesn't work... But how COULD I get this functionality to work? I know that the input value is indeed undefined, yet I need that to be recognized and change the input value. I know that array objects can be modified, but is there any way possible for me to assign the appropriate Boolean value inside of this if statement? Do I need to assign these variables inside of the if statement as so:

var oneInput = document.getElementById("someInput");

if (oneInput === undefined){
    var oneBoolean = false;
} else{
    var oneBoolean = true;
}

I don't believe that this would work either. Any help or pointers would be appreciated.