Fix jashkenas#4464: backticked expressions in class body should go in the initializer

Author: GeoffreyBooth

lib/coffeescript/nodes.js

@@ -1751,11 +1751,10 @@ exports.Class = class Class extends Base
       new Block expressions
 
   # Add an expression to the class initializer
-  #
-  # NOTE Currently, only methods and static methods are valid in ES class initializers.
-  # When additional expressions become valid, this method should be updated to handle them.
   addInitializerExpression: (node) ->
-    if @validInitializerMethod node
+    if node.unwrapAll() instanceof PassthroughLiteral
+      node
+    else if @validInitializerMethod node
       @addInitializerMethod node
     else
       null

src/nodes.coffee

@@ -1833,3 +1833,18 @@ test "#4591: super.x.y, super['x'].y", ->
   eq 2, b.t
   eq 2, b.s
   eq 2, b.r
+
+test "#4464: backticked expressions in class body", ->
+  class A
+    `get x() { return 42; }`
+
+  class B
+    `get x() { return 42; }`
+    constructor: ->
+      @y = 84
+
+  a = new A
+  eq 42, a.x
+  b = new B
+  eq 42, b.x
+  eq 84, b.y