smart way to detect current node

[redguardtoo]

(js2-node-abs-pos (js2-node-at-point (1- (point))))
(js2-node-len (js2-node-abs-pos (js2-node-at-point (1- (point)))))

test [1, 2, 3].slice(0,2)
maybe we can apply this into expand-region