Specifying project-local indentation settings via Projectionist

.projections.json

{
  "*.js": {
    "indent": "tabs:3"
  }
}

projectionist-indent.vim

autocmd User ProjectionistActivate call s:activate()
function! s:activate() abort
  for [root, value] in projectionist#query('indent')
    let l:pattern = '\v(tabs|spaces):(\d)'
    let l:matches = matchlist(value, l:pattern)
    if !empty(l:matches)
      let l:type = l:matches[1]
      let l:size = l:matches[2]
      if l:type ==? 'spaces'
        setlocal expandtab
      endif
      if l:type ==? 'tabs'
        setlocal noexpandtab
      endif
      let &l:tabstop     = l:size
      let &l:softtabstop = l:size
      let &l:shiftwidth  = l:size
    endif
    break
  endfor
endfunction