You can pass one parameter to the script using this notation:
[ScriptName](parameter)
and access it from the script, as a string type, with CurrentField.value
Using your example, the expression needs to be:
[f]_[test](value)
And the script:
function test() {
var dt = new Date();
var dx = dt.getDate() + CurrentField.value;
return dx
}
The parameter can be the result of another expression:
[ScriptName](1,5,3,[script2])
Because in this case it contains a separator, you can emulate passing multiple parameters:
var parameters=CurrentField.value.split(',');