Minimum code needed to get Volar working with eglot

init.el

(use-package eglot
  :config (add-to-list 'eglot-server-programs
                     '(web-mode . (eglot-volar "vue-language-server" "--stdio"))))

(defclass eglot-volar (eglot-lsp-server) ()
  :documentation "A custom class for Volar's langserver.")

;; Volar requires a path to a TypeScript SDK. It normally uses VSCode's preinstalled SDK.
;; tsdk is the correct variable as of https://github.com/johnsoncodehk/volar/pull/1916 being merged, but it may change at any time.
(cl-defmethod eglot-initialization-options ((server eglot-volar))
  "Passes through required Volar initialization options"
  (let* ((tsdk (concat (projectile-project-root) "node_modules/typescript/lib")))
    (list :typescript (list :tsdk (file-name-as-directory tsdk)))))