(js--continued-expression-p): Special-case unary plus and minus

* lisp/progmodes/js.el (js--continued-expression-p): Make an
effort to recognize unary plus and minus, in the contexts where
they make sense (https://github.com/mooz/js2-mode/issues/322).

lisp/progmodes/js.el

@@ -1770,7 +1770,11 @@ This performs fontification according to `js--class-styles'."
   "Return non-nil if the current line continues an expression."
   (save-excursion
     (back-to-indentation)
-    (or (js--looking-at-operator-p)
+    (if (js--looking-at-operator-p)
+        (or (not (memq (char-after) '(?- ?+)))
+            (progn
+              (forward-comment (- (point)))
+              (not (memq (char-before) '(?, ?\[ ?\()))))
       (and (js--re-search-backward "\n" nil t)
            (progn
              (skip-chars-backward " \t")

test/indent/js.js

@@ -95,6 +95,12 @@ Foobar
     console.log(num);
   });
 
+var arr = [
+  -1, 2,
+  -3, 4 +
+    -5
+];
+
 // Local Variables:
 // indent-tabs-mode: nil
 // js-indent-level: 2