How to send parameters to the JavaScript method that aren't constants?

(From my comment above) As an alternate/architectural suggestion, maybe consider creating a Javascript resource for each form (e.g. account.js, contact.js, etc.) and each of those files would define all the handlers for the respective form.

For example, your account.js file might look like this:

function form_onLoad() {
    // Do stuff on load.
}

function form_onSave() {
    // Do stuff on save.
}

function field_onChange() {
    executeSigning(param1, param2);
}

Now in the CRM handlers, you bind each event to its respective method. I have found this works well because it makes it easier to view/debug Javascript as everything is in one place and you don't have to view each handler in CRM.

You can send objects to JavaScript functions the same way as constants. To reference objects that are not in a form, you can give them and ID.

Element:

<div id="myelement">Hello</div>

Code:

// function
function jsfunc(variabelname)
{
    // dosomething with variabelname
}

// call function with reference to object
jsfunc( document.getElementById("myelement") );

You can also have a function without predefined parameters and access whatever is sent to the function via arguments.

Example:

function jsfunc()
{
    var output = "";
    var args = arguments;

    for(var i = 0, len = args.length; i < len; i++) // loop through all arguments
    {
        var arg = args[i]; // reference the argument directly
        output += i + ": "; // add index number
        if (arg == null)
        {
            output += "null"; // arg is null
        } else {
            output += typeof(arg) + ", "; // adds type of argument
            if (typeof(arg) == "string" || typeof(arg) == "number")
            {
                // argument is a string og number, which can be easily output
                output += arg;
            } else if (typeof(arg) == "object") {
                // it is an object
                if (arg.tagName)
                {
                    // the object has a tagname which means it's an HTML element
                    output += arg.tagName;
                } else {
                    // object but not HTML element, our array
                    output += "array, " + arg.firstname;
                }
            }
        }
        output += "\n"; // add new line
    }
    alert(output);
}

jsfunc(
    "a" /* type: string */
    , 5 /* type: number */
    , document.getElementById("txtFirstName") /* type object, has tagName INPUT */
    , document.getElementById("ElementThatDoesNotExists") /* type NULL */
    , { "firstname" : "john", "lastname" : "smith" } /* type object, no tagname */
);

Output:

0: string, a
1: number, 5
2: object, INPUT
3: null
4: object, array, john