Pressing Enter removes indentation

Question

If I have a file a.js like this:

let a1 = [
];

and I press Enter at the end of the first line, a Tab is inserted. I do not want this, so I added a setting:

filetype indent off

but then if I have this:

let a1 = [
   10,
   20
];

I have to manually add tabs for each item. So I added another setting:

set autoindent

These two settings solve the existing problems, but introduce a new problem.

If I move the cursor to the start of one of the indented lines, and press Enter the indentation is removed. Can I change a setting to resolve this issue?

To respond to an answer, I can use these settings:

filetype indent off
set smartindent

and redo the second example. However, after I press Enter, if I then press Up or Down, the indentation is removed, repeating the problem.

Answer 1

I think the setting set smartindent has the behavior you want.

If you use the following .vimrc on a.js, then you can see what's happening when you create a new line and press <cr> in normal mode while the cursor is over the indentation section of the new line.

I'm using the setting set list to make ends of lines visible (as $) and tabs visible (as ^I).

set list
filetype plugin on
filetype indent off
set smartindent

With this setting on, no tab is inserted in the first example.

let a1 = [$
$
];$

In the second example, a line beginning with some indentation characters is moved in a reasonable way

let a1 = [$
^I10,$
$
^I20$
];$

If you want the leading tab to be preserved in the middle line of the second example, then you can use I or [ ^ and then i ] to move your cursor to the first non-whitespace character.

If you start with the buffer below as a.js

let a1 = [$
^Ia1$
^I20$
];

And then type the command 3GI<cr>, then this will be the result.

let a1 = [$
^Ia1$
^I$
^I20$
];$

Answer 2

After trying the methods in the question, I then tried this:

filetype indent off
function F_indent()
   return indent(prevnonblank(v:lnum - 1))
endfunction
set indentexpr=F_indent()

http://vimdoc.sourceforge.net/htmldoc/eval.html#prevnonblank()

which passes the 2 tests in the question, but I noticed another problem. With the second example, if I put the cursor at the beginning of the last line and Press Enter, it inserts a Newline and a Tab. In addition, throughout these tests I have also noticed that all the previous methods remove indentation on empty lines:

How do I prevent Vim from unindenting empty lines?

So Ideally I wanted whatever I came up with to pass these tests:

1. whitespace removed only with backspace or delete
2. if cursor position greater than indent, match indent
3. if cursor position less or equal to indent, match position

To that end, I came up with this:

filetype indent off
function F_ind()
   let n_ind = indent(line('.'))
   let n_col = col('.') - 1
   if n_col > n_ind
      return "\n" . repeat("\t", n_ind / 3)
   else
      return "\n" . repeat("\t", n_col / 3)
   endif
endfunction
imap <expr> <CR> F_ind()

Note I use softtabstop=3, so adjust the / 3 as needed, or remove if you use hard tabs.