js-on-sx: Error/TypeError/etc return instance when called without new

lib/js/runtime.sx

@@ -817,27 +817,34 @@
       ((dict-has? obj "__proto__") (js-in-walk (get obj "__proto__") skey))
       (else false))))
 
+(define
+  js-error-init!
+  (fn
+    (this name args)
+    (begin
+      (dict-set!
+        this
+        "message"
+        (if (= (len args) 0) "" (js-to-string (nth args 0))))
+      (dict-set! this "name" name)
+      (dict-set! this "__js_error_data__" true)
+      this)))
+
+(define
+  js-error-receiver
+  (fn
+    (ctor)
+    (let
+      ((this (js-this)))
+      (cond
+        ((= (type-of this) "dict") this)
+        (else (js-new-call ctor (list)))))))
+
 (define
   Error
   (fn
     (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= (type-of this) "dict")
-          (do
-            (dict-set!
-              this
-              "message"
-              (if
-                (= (len args) 0)
-                ""
-                (js-to-string (nth args 0))))
-            (dict-set! this "name" "Error")
-            (dict-set! this "__js_error_data__" true))
-          nil)
-        this))))
+    (js-error-init! (js-error-receiver Error) "Error" args)))
 
 (define
   js-error-is-error
@@ -868,124 +875,28 @@
 
 (define
   TypeError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= (type-of this) "dict")
-          (do
-            (dict-set!
-              this
-              "message"
-              (if
-                (= (len args) 0)
-                ""
-                (js-to-string (nth args 0))))
-            (dict-set! this "name" "TypeError")
-            (dict-set! this "__js_error_data__" true))
-          nil)
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver TypeError) "TypeError" args)))
 (define
   RangeError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= (type-of this) "dict")
-          (do
-            (dict-set!
-              this
-              "message"
-              (if
-                (= (len args) 0)
-                ""
-                (js-to-string (nth args 0))))
-            (dict-set! this "name" "RangeError")
-            (dict-set! this "__js_error_data__" true))
-          nil)
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver RangeError) "RangeError" args)))
 (define
   SyntaxError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= (type-of this) "dict")
-          (do
-            (dict-set!
-              this
-              "message"
-              (if
-                (= (len args) 0)
-                ""
-                (js-to-string (nth args 0))))
-            (dict-set! this "name" "SyntaxError")
-            (dict-set! this "__js_error_data__" true))
-          nil)
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver SyntaxError) "SyntaxError" args)))
 (define
   ReferenceError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= (type-of this) "dict")
-          (do
-            (dict-set!
-              this
-              "message"
-              (if
-                (= (len args) 0)
-                ""
-                (js-to-string (nth args 0))))
-            (dict-set! this "name" "ReferenceError")
-            (dict-set! this "__js_error_data__" true))
-          nil)
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver ReferenceError) "ReferenceError" args)))
 (define
   URIError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= this :js-undefined)
-          nil
-          (do
-            (dict-set!
-              this
-              "message"
-              (if (empty? args) "" (js-to-string (nth args 0))))
-            (dict-set! this "name" "URIError")
-            (dict-set! this "__js_error_data__" true)))
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver URIError) "URIError" args)))
 (define
   EvalError
-  (fn
-    (&rest args)
-    (let
-      ((this (js-this)))
-      (begin
-        (if
-          (= this :js-undefined)
-          nil
-          (do
-            (dict-set!
-              this
-              "message"
-              (if (empty? args) "" (js-to-string (nth args 0))))
-            (dict-set! this "name" "EvalError")
-            (dict-set! this "__js_error_data__" true)))
-        this))))
+  (fn (&rest args)
+    (js-error-init! (js-error-receiver EvalError) "EvalError" args)))
 
 (define AggregateError :js-undefined)
 

plans/js-on-sx.md

@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-09 — **`Error(msg)` / `TypeError(msg)` / etc. (called without `new`) now return a proper instance.** Was checking `(if (= (type-of this) "dict") <init> nil)` and falling through to return undefined when called as a plain function — but per spec, every Error subclass must return a new instance regardless of `new`. Refactored each constructor to `(js-error-init! (js-error-receiver Ctor) "Name" args)`: `js-error-receiver` returns `this` if it's a dict (the `new`-call case) and otherwise re-enters via `js-new-call ctor (list)` to create a properly-prototyped instance; `js-error-init!` sets `message`, `name`, `__js_error_data__`. Cleaner than the seven near-identical duplicated bodies. Result: built-ins/Error 17/30 → 22/30 (+5), language/expressions/instanceof 18/30 → 20/30. NativeErrors holds at 27/30. conformance.sh: 148/148.
+
 - 2026-05-09 — **`typeof <undeclaredIdent>` returns `"undefined"` instead of throwing ReferenceError.** Per JS spec, `typeof` on an unresolvable Reference is special-cased — it must return `"undefined"` without throwing. We were transpiling `typeof X` to `(js-typeof <symbol-X>)`, and the symbol lookup itself errored for undeclared globals. New transpiler branch in `js-transpile-unop`: when the operand is a `js-ident`, emit `(if (or (env-has? (current-env) "name") (dict-has? js-global "name")) (js-typeof <name>) "undefined")` — checks both the lexical env (for local var/let/const/parameters) and the global object, and only references the symbol when the if branch is taken (SX `if` is lazy, so the unbound symbol in the false branch never errors). Result: language/expressions/typeof 9/13 → 10/13, built-ins/Object 29/30 → 30/30 (full pass — the `S15.2.1.1_A2_T11.js` test was using `typeof obj` on an undeclared name). conformance.sh: 148/148.
 
 - 2026-05-09 — **`==` returns false when either side is NaN, even across the numeric/string paths.** `js-loose-eq` was converting both sides to numbers (`Number.NaN == "string"` → `NaN == NaN`) and using SX `(=)`, which apparently returns true when both NaN values are the same reference. Per JS, NaN compares unequal to everything including itself. Wrapped both cross-type numeric/string branches in `(or (js-number-is-nan an) (js-number-is-nan bn))` short-circuits to false. Result: language/expressions/equals 20/30 → 23/30. strict-equals/Number/Object unchanged. conformance.sh: 148/148.