sample

a.lua

local lapi = require'lapi'

local SELECTOR = {
  markers = { 'package.json' },
  filetypes = { 'javascript', 'typescript', 'javascript.jsx', 'typescript.tsx' },
}

lapi.extensions.register('eslint', {

  is = function(document)
    return document.is(SELECTOR)
  end,

  activate = function(extension)
    assert(vim.loop.exepath('eslint'), 'should install eslint for your path.')

    extension.attach(lapi.completion.register('eslint', {
      is = function(document)
        return document.is(SELECTOR)
      end,
      metadata = function()
      end,
      datermine = function()
      end,
      complete = function()
      end,
      resolve = function()
      end,
    }))

    extension.attach(lapi.workspace.on_text_document_did_open(function(event)
      local document = event.document
      if not document.is(SELECTOR) then
        return
      end
    end))

    return extension
  end,

})