js-on-sx: delete operator

js-transpile-unop intercepts 'delete' before transpiling the
operand. Maps to (js-delete-prop obj key) for members and indexed
access. Runtime js-delete-prop sets the dict value to js-undefined
and returns true.

444/446 unit (+2), 148/148 slice unchanged.

lib/js/runtime.sx

@@ -1825,6 +1825,15 @@
 
 (define Object {:entries js-object-entries :values js-object-values :freeze js-object-freeze :assign js-object-assign :keys js-object-keys})
 
+(define
+  js-delete-prop
+  (fn
+    (obj key)
+    (cond
+      ((dict? obj)
+        (begin (dict-set! obj (js-to-string key) js-undefined) true))
+      (else true))))
+
 (define
   js-optchain-get
   (fn

lib/js/test.sh

@@ -1141,6 +1141,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3201)
 (eval "(js-eval \"var {aa: x2, bb: y2} = {aa:1, bb:2}; x2+y2\")")
 
+;; ── Phase 11.delete ────────────────────────────────────────────
+(epoch 3300)
+(eval "(js-eval \"var o = {x: 5}; delete o.x; o.x === undefined\")")
+(epoch 3301)
+(eval "(js-eval \"var o = {a:1, b:2}; delete o.a; o.b\")")
+
 EPOCHS
 
 
@@ -1760,6 +1766,10 @@ check 3101 "rest arr join"                 '"2,3,4"'
 check 3200 "obj rename"                    '100'
 check 3201 "obj multi rename"              '3'
 
+# ── Phase 11.delete ───────────────────────────────────────────
+check 3300 "delete obj.x"                  'true'
+check 3301 "delete obj.a keeps b"         '2'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "✓ $PASS/$TOTAL JS-on-SX tests passed"

lib/js/transpile.sx

@@ -165,16 +165,31 @@
   js-transpile-unop
   (fn
     (op arg)
-    (let
-      ((a (js-transpile arg)))
-      (cond
-        ((= op "-") (list (js-sym "js-neg") a))
-        ((= op "+") (list (js-sym "js-pos") a))
-        ((= op "!") (list (js-sym "js-not") a))
-        ((= op "~") (list (js-sym "js-bitnot") a))
-        ((= op "typeof") (list (js-sym "js-typeof") a))
-        ((= op "void") (list (js-sym "quote") :js-undefined))
-        (else (error (str "js-transpile-unop: unsupported op: " op)))))))
+    (cond
+      ((= op "delete")
+        (cond
+          ((js-tag? arg "js-member")
+            (list
+              (js-sym "js-delete-prop")
+              (js-transpile (nth arg 1))
+              (nth arg 2)))
+          ((js-tag? arg "js-index")
+            (list
+              (js-sym "js-delete-prop")
+              (js-transpile (nth arg 1))
+              (js-transpile (nth arg 2))))
+          (else true)))
+      (else
+        (let
+          ((a (js-transpile arg)))
+          (cond
+            ((= op "-") (list (js-sym "js-neg") a))
+            ((= op "+") (list (js-sym "js-pos") a))
+            ((= op "!") (list (js-sym "js-not") a))
+            ((= op "~") (list (js-sym "js-bitnot") a))
+            ((= op "typeof") (list (js-sym "js-typeof") a))
+            ((= op "void") (list (js-sym "quote") :js-undefined))
+            (else (error (str "js-transpile-unop: unsupported op: " op)))))))))
 
 ;; ── Binary ops ────────────────────────────────────────────────────