You can of course continue to utilize the Classic Designer, and any code created in there for Version 10 should continue to work on Version 11.

But the New Designer is an entirely different animal when it comes to scripting.  For a few reasons:

1. The new designer doesn't utilize JQuery like the classic designer does, so any code needs to be re-written in vanilla Javascript.
2. The Javascript runs within a Sandboxed iFrame, so it doesn't have direct access to the structure of the Form/Window/Document/Fields/etc.  That means you are limited to changes that can be applied using the LFForm interface.  They keep adding more to the LFForm interface, but it is still going to be a lot more limited than what we could code in the Classic Designer.
3. The structure of the form is no longer dictated solely by the DOM structure as the "source-of-truth", but rather uses Angular as the internal source of truth - so even if we could edit the structure, the changes wouldn't "stick".

There's a comment by a Laserfiche employee on this post, that explains it really well.

For purposes of making the form function better on different devices and security of the form, the changes to the new designer are tremendous and very helpful.  And there are some really fantastic changes with things like Field Rules.  But the trade-off is there are still limitations in what we can code in the new designer that we were used to being able to do in the classic designer.

Here's some notes on your specific requests:

• Title, that displays name of the form in browser:

  • There have been multiple requests for this functionality, but as of the current release (Forms 11 Update 5 / Version 11.0.2311) this isn't currently possible.

• Phone and SSN masking

  • There is now built-in functionality that can handle much of this as of the current release (Forms 11 Update 5 / Version 11.0.2311).  There was also some code shared on this post that worked in Forms 11 Update 3 / Version 11.0.2212.

• Proper capitalization

  • This should still be possible via Javascript, but the code will need to be rewritten to utilize the LFForm interface in vanilla Javascript.

• Restrict negative numbers

  • There is now built-in functionality that can handle much of this as of the current release (Forms 11 Update 5 / Version 11.0.2311).

EDIT TO ADD: Here is the "Proper Capitalization" script re-written for the New Designer (tested on Forms 11 Update 5 / Version 11.0.2311): 

var capitalizeMe = LFForm.findFieldsByClassName("capitalizeMe");
capitalizeMe.forEach(function(el) {
  LFForm.onFieldBlur(function(e) {
    var orig = LFForm.getFieldValues(e.options[0]);
    var breakSpaces = orig.split(' ');
    var newWords = [];
    breakSpaces.forEach(function(word) {
      newWords.push(word.charAt(0).toUpperCase() + word.slice(1));
    });
    var newValue = newWords.join(' ');
    LFForm.setFieldValues(e.options[0], newValue);
  }, el);
});