Fixes #2323. Fixes #2148.

compiler/jsgen.nim

@@ -961,18 +961,18 @@ proc genAddr(p: PProc, n: PNode, r: var TCompRes) =
   of nkCheckedFieldExpr:
     genCheckedFieldAddr(p, n, r)
   of nkDotExpr:
-    genFieldAddr(p, n, r)
+    genFieldAddr(p, n.sons[0], r)
   of nkBracketExpr:
     var ty = skipTypes(n.sons[0].typ, abstractVarRange)
     if ty.kind in {tyRef, tyPtr}: ty = skipTypes(ty.lastSon, abstractVarRange)
     case ty.kind
     of tyArray, tyArrayConstr, tyOpenArray, tySequence, tyString, tyCString,
-       tyVarargs:
+       tyVarargs, tyChar:
-      genArrayAddr(p, n, r)
+      genArrayAddr(p, n.sons[0], r)
     of tyTuple:
-      genFieldAddr(p, n, r)
+      genFieldAddr(p, n.sons[0], r)
-    else: internalError(n.info, "expr(nkBracketExpr, " & $ty.kind & ')')
+    else: internalError(n.sons[0].info, "expr(nkBracketExpr, " & $ty.kind & ')')
-  else: internalError(n.info, "genAddr")
+  else: internalError(n.sons[0].info, "genAddr")
 
 proc genSym(p: PProc, n: PNode, r: var TCompRes) =
   var s = n.sym

lib/system/jssys.nim

@@ -563,7 +563,11 @@ proc nimCopy(x: pointer, ti: PNimType): pointer =
       }
     """
   of tyString:
-    asm "`result` = `x`.slice(0);"
+    asm """
+      if (`x` !== null) {
+        `result` = `x`.slice(0);
+      }
+    """
   else:
     result = x
 

tests/js/taddr.nim

@@ -0,0 +1,36 @@
+type T = object
+  x: int
+  s: string
+
+var obj: T
+var fieldAddr = addr(obj.x)
+var objAddr = addr(obj)
+
+# Integer tests
+var field = fieldAddr[]
+doAssert field == 0
+
+var objDeref = objAddr[]
+doAssert objDeref.x == 0
+
+# Change value
+obj.x = 42
+
+doAssert field == 0
+doAssert objDeref.x == 0
+
+field = fieldAddr[]
+objDeref = objAddr[]
+
+doAssert field == 42
+doAssert objDeref.x == 42
+
+# String tests
+obj.s = "lorem ipsum dolor sit amet"
+var indexAddr = addr(obj.s[2])
+
+doAssert indexAddr[] == '4'
+
+indexAddr[] = 'd'
+
+doAssert indexAddr[] == 'd'