How to remove any JavaScript code From a Dom element

Question: How to remove any JavaScript code (functions, variables, events etc.) which is Inside a Dom element (div)

Note: This is not similar question like removing content from Dom element.

My Scenario:

My site has a menu. When I click on a menu item I am loading corresponding html file which also contains JavaScript code inside a div element(id=content).
When click on menu I am doing following code

function changeMenu(params){
  //need something here to remove previous js codes before load the file
  $('#content').load(params['file'],function (){
        ///ohters code
    })
}

It is working fine for first click and executing the JavaScript code as well inside that file.
But problem is it also increase executing JavaScript code number of times I click on the menu. Also when I load another file still previous JavaScript code executing because I had interval function there. Aslo if there is variable declared like this let x=10
it showing follwing error when I click the menu again

Uncaught SyntaxError: Identifier ‘x’ has already been declared

Asking Solution:
Is it posible remove all JavaScript codes when I click on the menu and How?