js toggle implementation

js.el

(defun js-jump-to (current from to format-name)
  (find-file
   (cl-loop with parts = (reverse current)
            with fname = (file-name-sans-extension (cl-first parts))
            for (name . rest) on (cl-rest parts)
            until (string-equal name from)
            collect name into names
            finally (cl-return
                     (mapconcat 'identity
                                (nconc (reverse rest)
                                       (list to)
                                       (reverse names)
                                       (list (funcall format-name fname) )) "/" )))))

(defun js-format-impl-name (fname)
  (format "%s.js" (replace-regexp-in-string "Spec" "" fname)))

(defun js-format-test-name (fname)
  (format "%sSpec.js" fname))

(defun js-jump-to-implementation-or-test ()
  (interactive)
  (let ((current (split-string (buffer-file-name) "/")))
    (cond
     ((member "test" current) (js-jump-to current "test" "lib" 'js-format-impl-name))
     ((member "lib" current)  (js-jump-to current "lib" "test" 'js-format-test-name))
     (t (error "not within a test or lib directory"))
  )))

├── src
│   └── js
│       └── foo.js
└── test
      └── foo_test.js

Hi Mike. As you can see my project tree is different. Could you please help me to make this work for me? I don't know lisp. Thank you