fixes #20227; skip distinct types for genObjConstr [JS backend] (#20229)

fixes #20227; skip distinct types for genObjConstr

compiler/jsgen.nim

@@ -2272,6 +2272,7 @@ proc genObjConstr(p: PProc, n: PNode, r: var TCompRes) =
   r.kind = resExpr
   var initList : Rope
   var fieldIDs = initIntSet()
+  let nTyp = n.typ.skipTypes(abstractInst)
   for i in 1..<n.len:
     if i > 1: initList.add(", ")
     var it = n[i]
@@ -2280,7 +2281,7 @@ proc genObjConstr(p: PProc, n: PNode, r: var TCompRes) =
     gen(p, val, a)
     var f = it[0].sym
     if f.loc.r == nil: f.loc.r = mangleName(p.module, f)
-    fieldIDs.incl(lookupFieldAgain(n.typ, f).id)
+    fieldIDs.incl(lookupFieldAgain(nTyp, f).id)
 
     let typ = val.typ.skipTypes(abstractInst)
     if a.typ == etyBaseIndex:

tests/stdlib/tmisc_issues.nim

@@ -0,0 +1,17 @@
+discard """
+  targets: "c cpp js"
+"""
+
+# bug #20227
+type
+  Data = object
+    id: int
+
+  Test = distinct Data
+
+  Object = object
+    data: Test
+
+
+var x: Object = Object(data: Test(Data(id: 12)))
+doAssert Data(x.data).id == 12