Use smarter newline mapping for json filetype

.config/nvim/ftplugin/json.lua

@@ -0,0 +1,19 @@
+local json_newline = function()
+  local line = vim.api.nvim_get_current_line()
+  if line == "" then
+    print("line is empty")
+    return "o"
+  elseif string.byte(line, -1) == string.byte(",") then
+    return "o"
+  elseif string.byte(line, -1) == string.byte("{") then
+    print("line ends with '{'")
+    return "o"
+  elseif string.byte(line, -1) == string.byte("}") then
+    print("line ends with '}'")
+    return "o"
+  else
+    return "A,<CR>"
+  end
+end
+
+vim.keymap.set("n", "o", json_newline, { buffer = true, expr = true })