How to prevent losing indentation when editing JavaScript code within HTML files in Emacs?

Question

When I edit JavaScript code which exists in an HTML file, I lose code indentation whenever I press Enter.

first line of code:
    second line of code # Press Enter here

Result after pressing Enter:

first line of code
second line of code

(the indentation is lost)

How to prevent this?
P.S. I am using Emacs 25

Answer 1

That's due to electric-indent-mode, which is a global minor mode.

You could add (electric-indent-mode -1) to your init file to disable it entirely, or you could try using a custom electric-indent-functions function.

The following is only minimally tested, but might do the trick:

(add-hook 'html-mode-hook 'my-html-mode-hook)

(defun my-html-mode-hook ()
  "Custom `html-mode' behaviours."
  (add-hook 'electric-indent-functions
            'my-html-mode-electric-indent-maybe nil :local))

(defun my-html-mode-electric-indent-maybe (_char)
  "Used in `electric-indent-functions'."
  (save-excursion
    (when (ignore-errors
            (string= (sgml-tag-name (sgml-parse-tag-backward))
                     "script"))
      'no-indent)))

Answer 2

It seems this bug is related to Emacs 25 because when I upgraded to version 25, I no longer am facing this problem.