diff --git a/crates/oxide_emit/src/expr/operator/mod.rs b/crates/oxide_emit/src/expr/operator/mod.rs
index d62d754..9dc8799 100644
--- a/crates/oxide_emit/src/expr/operator/mod.rs
+++ b/crates/oxide_emit/src/expr/operator/mod.rs
@@ -62,7 +62,12 @@ impl Emitter {
         if matches!(un.operator, UnaryOperator::Delete) {
             return match &un.argument {
                 Expression::Identifier(_) => {
-                    Err("SyntaxError: delete of an unqualified identifier in strict mode".into())
+                    // 严格模式的 delete 标识符由 oxc_semantic 提前拦截为早期错误；
+                    // 非严格语义返回 false（标识符不可删除）。
+                    let idx = ctx.add_constant(Constant::Boolean(false));
+                    let reg = ctx.alloc_reg();
+                    ctx.inst(Inst::load_const(Operand::Reg(reg), idx));
+                    Ok(reg)
                 }
                 Expression::StaticMemberExpression(member) => {
                     let obj_reg = self.emit_expression(&member.object, ctx)?;
diff --git a/crates/oxide_parser/Cargo.toml b/crates/oxide_parser/Cargo.toml
index 5173bf6..339dce4 100644
--- a/crates/oxide_parser/Cargo.toml
+++ b/crates/oxide_parser/Cargo.toml
@@ -13,3 +13,4 @@ oxc_ast.workspace = true
 oxc_span.workspace = true
 oxc_diagnostics.workspace = true
 oxc_syntax.workspace = true
+oxc_semantic = "0.134.0"
diff --git a/crates/oxide_parser/src/lib.rs b/crates/oxide_parser/src/lib.rs
index 4682fe6..1a3e477 100644
--- a/crates/oxide_parser/src/lib.rs
+++ b/crates/oxide_parser/src/lib.rs
@@ -20,7 +20,7 @@ pub fn parse<'a>(allocator: &'a Allocator, source: &'a str) -> Result<Program<'a
     use oxc_parser::Parser;
     use oxc_span::SourceType;
 
-    let source_type = SourceType::default();
+    let source_type = SourceType::unambiguous();
     let ret = Parser::new(allocator, source, source_type).parse();
 
     if ret.panicked {
@@ -34,5 +34,13 @@ pub fn parse<'a>(allocator: &'a Allocator, source: &'a str) -> Result<Program<'a
         return Err(ret.errors.into_iter().map(OxideError::from).collect());
     }
 
+    // 语法早期错误（Early Errors）检查：oxc parser 把复杂早期错误委托给
+    // oxc_semantic（strict 绑定标识符、重复参数、NSPL、super 位置等）。
+    let semantic_ret =
+        oxc_semantic::SemanticBuilder::new().with_check_syntax_error(true).build(&ret.program);
+    if !semantic_ret.errors.is_empty() {
+        return Err(semantic_ret.errors.into_iter().map(OxideError::from).collect());
+    }
+
     Ok(ret.program)
 }
diff --git a/crates/oxide_test262/src/main.rs b/crates/oxide_test262/src/main.rs
index cb1c5a6..106326c 100644
--- a/crates/oxide_test262/src/main.rs
+++ b/crates/oxide_test262/src/main.rs
@@ -268,12 +268,20 @@ fn append_source_chunk(out: &mut String, name: &str, source: &str) {
 
 /// 取测试元数据的 harness 缓存键（即其 `includes` 列表）。
 fn harness_key(meta: &TestMeta) -> Vec<String> {
-    meta.includes.clone()
+    let mut key = meta.includes.clone();
+    if meta.flags.iter().any(|f| f == "onlyStrict") {
+        key.push("__onlyStrict__".into());
+    }
+    key
 }
 
 /// 按测试元数据拼接完整的 harness 前缀源码（prelude + sta/assert + 各 include）。
 fn build_harness_source(meta: &TestMeta, harness: &HarnessSources) -> Result<String, String> {
     let mut source = String::new();
+    // onlyStrict 测试在严格模式下运行：指令必须位于脚本最前（harness 之前）。
+    if meta.flags.iter().any(|f| f == "onlyStrict") {
+        append_source_chunk(&mut source, "use strict", "\"use strict\";");
+    }
     append_source_chunk(&mut source, "Test262Error prelude", test262_error_prelude());
     append_source_chunk(
         &mut source,