java script function disappear after clicking on submit button

Solution 1:

Your GetNewMap method does not prevent the default action. You display a new map, and then the form is submitted to the server, and your new map will disappear.

You need to prevent the form from being submitted:

<form method="get" name="mynewMap" onsubmit="GetNewMap(event)"> 

function GetNewMap(e) {
    e.preventDefault();
    ...

Event.preventDefault() - Web APIs | MDN

As pointed out in the comments, the alternative is to change your <button type="submit" to a <button type="button", which would not submit the form. In that case, you would need to handle the button's click event rather than the form's submit event.