How to Auto refresh a Page when a Dropdown value is changed

Hi

My scenario is I have a Dropdown where a User can choose between 2 values.
Based on the users choice, I perform some JavaScript operation and display some result.
This is fairly straightforward.
But If the user changes the value in the Drop Down , then the Result does not reflect the new change.
I have to manually refresh the page to reset all the variables and then choose the new dropdown value.
I understand the the JavaScript function is called only once and the value is set based on users choice.
But Upon changing the Dropdown value, the JavaScript function is not called again, hence the new change is not reflected.
If I attach a form Variable with the Dropdown then I can see the change instantly, but here I cannot perform the manipulation of the value.
I am just using the options available inside the designer form. I am not using any Custom Widget here.

Is there a way to Refresh the value everytime the user changes the Dropdown value.

Thanks