diff --git a/crates/oxide_builtins/src/array/immutable.rs b/crates/oxide_builtins/src/array/immutable.rs
new file mode 100644
index 00000000..04635a07
--- /dev/null
+++ b/crates/oxide_builtins/src/array/immutable.rs
@@ -0,0 +1,179 @@
+use oxide_types::value::JsValue;
+
+use oxide_runtime_api::{NativeResult, VmHost};
+
+use crate::builtins_debug;
+
+use super::common::{
+    arraylike_get, arraylike_get_or_err, check_array_create_len, create_new_array, get_this_arraylike,
+};
+use super::from::from_engine_error;
+use super::sort_iterator::{parse_sort_comparator, sort_values_inner};
+
+/// Array.prototype.toReversed()：返回元素逆序的新数组，原数组不变。
+pub fn array_to_reversed<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    builtins_debug!("Array.prototype.toReversed called with {} args", args.len());
+    let this_val = vm.reg(args[0]);
+    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
+        Ok(v) => v,
+        Err(err) => return NativeResult::Err(err),
+    };
+    let new_arr = create_new_array(vm, n);
+    if let Err(err) = check_array_create_len(vm, n) {
+        return NativeResult::Err(err);
+    }
+    // ????????????????getter ???????????
+    for i in (0..n).rev() {
+        let elem = arraylike_get_or_err!(vm, arr_ptr, i);
+        unsafe {
+            (*new_arr).set_prop_at(n - 1 - i, elem);
+        }
+    }
+    NativeResult::Ok(JsValue::from_js_object(new_arr))
+}
+
+/// Array.prototype.with(index, value)：返回把指定下标替换为新值的新数组，原数组不变。
+pub fn array_with<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    builtins_debug!("Array.prototype.with called with {} args", args.len());
+    let this_val = vm.reg(args[0]);
+    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
+        Ok(v) => v,
+        Err(err) => return NativeResult::Err(err),
+    };
+    let index_val = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
+    let idx = match vm.coerce_number_bounded(index_val) {
+        Ok(v) => v,
+        Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
+    };
+    // ToIntegerOrInfinity：NaN/-0/+0 -> 0，其余截断。
+    let rel = if idx.is_nan() || idx == 0.0 { 0.0 } else { idx.trunc() };
+    let actual = if rel < 0.0 { n as f64 + rel } else { rel };
+    if actual < 0.0 || actual >= n as f64 {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid index for Array.prototype.with"));
+    }
+    let actual_idx = actual as usize;
+    let value = if args.len() > 2 { vm.reg(args[2]) } else { JsValue::undefined() };
+    if let Err(err) = check_array_create_len(vm, n) {
+        return NativeResult::Err(err);
+    }
+    let new_arr = create_new_array(vm, n);
+    for i in 0..n {
+        // 规范：被替换位置不执行 Get。
+        let elem = if i == actual_idx { value } else { arraylike_get_or_err!(vm, arr_ptr, i) };
+        unsafe {
+            (*new_arr).set_prop_at(i, elem);
+        }
+    }
+    NativeResult::Ok(JsValue::from_js_object(new_arr))
+}
+pub fn array_to_sorted<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    builtins_debug!("Array.prototype.toSorted called with {} args", args.len());
+    // 规范先校验 compareFn 可调用，再读取 this/length。
+    let comparator = if args.len() > 1 {
+        match parse_sort_comparator(vm, vm.reg(args[1])) {
+            Ok(c) => c,
+            Err(err) => return NativeResult::Err(err),
+        }
+    } else {
+        None
+    };
+    let this_val = vm.reg(args[0]);
+    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
+        Ok(v) => v,
+        Err(err) => return NativeResult::Err(err),
+    };
+    if let Err(err) = check_array_create_len(vm, n) {
+        return NativeResult::Err(err);
+    }
+    let mut vals: Vec<JsValue> = match (0..n)
+        .map(|i| arraylike_get(vm, arr_ptr, i))
+        .collect::<Result<Vec<JsValue>, JsValue>>()
+    {
+        Ok(v) => v,
+        Err(err) => return NativeResult::Err(err),
+    };
+    if let Err(err) = sort_values_inner(vm, &mut vals, comparator) {
+        return NativeResult::Err(err);
+    }
+    let new_arr = create_new_array(vm, n);
+    for (i, &v) in vals.iter().enumerate() {
+        unsafe {
+            (*new_arr).set_prop_at(i, v);
+        }
+    }
+    NativeResult::Ok(JsValue::from_js_object(new_arr))
+}
+pub fn array_to_spliced<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    builtins_debug!("Array.prototype.toSpliced called with {} args", args.len());
+    let this_val = vm.reg(args[0]);
+    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
+        Ok(v) => v,
+        Err(err) => return NativeResult::Err(err),
+    };
+    let relative_start = if args.len() > 1 {
+        match vm.coerce_number_bounded(vm.reg(args[1])) {
+            Ok(v) => v,
+            Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
+        }
+    } else {
+        0.0
+    };
+    let relative_start = if relative_start.is_nan() { 0.0 } else { relative_start.trunc() };
+    let actual_start = if relative_start < 0.0 {
+        (n as f64 + relative_start).max(0.0) as usize
+    } else {
+        relative_start.min(n as f64) as usize
+    };
+    // 缺省规则：start 与 deleteCount 都缺省 -> 拷贝；仅缺省 deleteCount -> 删到末尾。
+    let delete_count = if args.len() <= 1 {
+        0
+    } else if args.len() == 2 {
+        n - actual_start
+    } else {
+        let dc = match vm.coerce_number_bounded(vm.reg(args[2])) {
+            Ok(v) => v,
+            Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
+        };
+        let dc = if dc.is_nan() || dc <= 0.0 { 0 } else { dc.trunc() as usize };
+        dc.min(n - actual_start)
+    };
+    let insert_count = if args.len() > 3 { args.len() - 3 } else { 0 };
+    // ???newLen = len + insertCount - actualDeleteCount?> 2**53-1 ? TypeError?
+    // ArrayCreate(newLen) ? 2**32-1 ? RangeError??????/???????
+    let new_len = n.saturating_add(insert_count).saturating_sub(delete_count);
+    if new_len > 9_007_199_254_740_991 {
+        return NativeResult::Err(crate::error::create_type_error(vm, "Invalid array length"));
+    }
+    if let Err(err) = check_array_create_len(vm, new_len) {
+        return NativeResult::Err(err);
+    }
+    let mut out: Vec<JsValue> = Vec::with_capacity(new_len);
+    out.extend(
+        match (0..actual_start)
+            .map(|i| arraylike_get(vm, arr_ptr, i))
+            .collect::<Result<Vec<JsValue>, JsValue>>()
+        {
+            Ok(v) => v,
+            Err(err) => return NativeResult::Err(err),
+        },
+    );
+    for k in 0..insert_count {
+        out.push(vm.reg(args[3 + k]));
+    }
+    out.extend(
+        match (actual_start + delete_count..n)
+            .map(|i| arraylike_get(vm, arr_ptr, i))
+            .collect::<Result<Vec<JsValue>, JsValue>>()
+        {
+            Ok(v) => v,
+            Err(err) => return NativeResult::Err(err),
+        },
+    );
+    let new_arr = create_new_array(vm, out.len());
+    for (i, &v) in out.iter().enumerate() {
+        unsafe {
+            (*new_arr).set_prop_at(i, v);
+        }
+    }
+    NativeResult::Ok(JsValue::from_js_object(new_arr))
+}
diff --git a/crates/oxide_builtins/src/array/mod.rs b/crates/oxide_builtins/src/array/mod.rs
index b2ab2f9e..52e2f0f4 100644
--- a/crates/oxide_builtins/src/array/mod.rs
+++ b/crates/oxide_builtins/src/array/mod.rs
@@ -1,9 +1,3 @@
-use oxide_types::value::JsValue;
-
-use oxide_runtime_api::{NativeResult, VmHost};
-
-use crate::builtins_debug;
-
 mod common;
 pub(crate) use common::*;
 
@@ -19,170 +13,5 @@ pub use iterate::*;
 mod sort_iterator;
 pub use sort_iterator::*;
 
-/// Array.prototype.toReversed()：返回元素逆序的新数组，原数组不变。
-pub fn array_to_reversed<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
-    builtins_debug!("Array.prototype.toReversed called with {} args", args.len());
-    let this_val = vm.reg(args[0]);
-    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
-        Ok(v) => v,
-        Err(err) => return NativeResult::Err(err),
-    };
-    let new_arr = create_new_array(vm, n);
-    if let Err(err) = check_array_create_len(vm, n) {
-        return NativeResult::Err(err);
-    }
-    // ????????????????getter ???????????
-    for i in (0..n).rev() {
-        let elem = arraylike_get_or_err!(vm, arr_ptr, i);
-        unsafe {
-            (*new_arr).set_prop_at(n - 1 - i, elem);
-        }
-    }
-    NativeResult::Ok(JsValue::from_js_object(new_arr))
-}
-
-/// Array.prototype.with(index, value)：返回把指定下标替换为新值的新数组，原数组不变。
-pub fn array_with<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
-    builtins_debug!("Array.prototype.with called with {} args", args.len());
-    let this_val = vm.reg(args[0]);
-    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
-        Ok(v) => v,
-        Err(err) => return NativeResult::Err(err),
-    };
-    let index_val = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
-    let idx = match vm.coerce_number_bounded(index_val) {
-        Ok(v) => v,
-        Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
-    };
-    // ToIntegerOrInfinity：NaN/-0/+0 -> 0，其余截断。
-    let rel = if idx.is_nan() || idx == 0.0 { 0.0 } else { idx.trunc() };
-    let actual = if rel < 0.0 { n as f64 + rel } else { rel };
-    if actual < 0.0 || actual >= n as f64 {
-        return NativeResult::Err(crate::error::create_range_error(vm, "invalid index for Array.prototype.with"));
-    }
-    let actual_idx = actual as usize;
-    let value = if args.len() > 2 { vm.reg(args[2]) } else { JsValue::undefined() };
-    if let Err(err) = check_array_create_len(vm, n) {
-        return NativeResult::Err(err);
-    }
-    let new_arr = create_new_array(vm, n);
-    for i in 0..n {
-        // 规范：被替换位置不执行 Get。
-        let elem = if i == actual_idx { value } else { arraylike_get_or_err!(vm, arr_ptr, i) };
-        unsafe {
-            (*new_arr).set_prop_at(i, elem);
-        }
-    }
-    NativeResult::Ok(JsValue::from_js_object(new_arr))
-}
-pub fn array_to_sorted<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
-    builtins_debug!("Array.prototype.toSorted called with {} args", args.len());
-    // 规范先校验 compareFn 可调用，再读取 this/length。
-    let comparator = if args.len() > 1 {
-        match parse_sort_comparator(vm, vm.reg(args[1])) {
-            Ok(c) => c,
-            Err(err) => return NativeResult::Err(err),
-        }
-    } else {
-        None
-    };
-    let this_val = vm.reg(args[0]);
-    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
-        Ok(v) => v,
-        Err(err) => return NativeResult::Err(err),
-    };
-    if let Err(err) = check_array_create_len(vm, n) {
-        return NativeResult::Err(err);
-    }
-    let mut vals: Vec<JsValue> = match (0..n)
-        .map(|i| arraylike_get(vm, arr_ptr, i))
-        .collect::<Result<Vec<JsValue>, JsValue>>()
-    {
-        Ok(v) => v,
-        Err(err) => return NativeResult::Err(err),
-    };
-    if let Err(err) = sort_values_inner(vm, &mut vals, comparator) {
-        return NativeResult::Err(err);
-    }
-    let new_arr = create_new_array(vm, n);
-    for (i, &v) in vals.iter().enumerate() {
-        unsafe {
-            (*new_arr).set_prop_at(i, v);
-        }
-    }
-    NativeResult::Ok(JsValue::from_js_object(new_arr))
-}
-pub fn array_to_spliced<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
-    builtins_debug!("Array.prototype.toSpliced called with {} args", args.len());
-    let this_val = vm.reg(args[0]);
-    let (arr_ptr, n, _is_array) = match get_this_arraylike(vm, this_val) {
-        Ok(v) => v,
-        Err(err) => return NativeResult::Err(err),
-    };
-    let relative_start = if args.len() > 1 {
-        match vm.coerce_number_bounded(vm.reg(args[1])) {
-            Ok(v) => v,
-            Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
-        }
-    } else {
-        0.0
-    };
-    let relative_start = if relative_start.is_nan() { 0.0 } else { relative_start.trunc() };
-    let actual_start = if relative_start < 0.0 {
-        (n as f64 + relative_start).max(0.0) as usize
-    } else {
-        relative_start.min(n as f64) as usize
-    };
-    // 缺省规则：start 与 deleteCount 都缺省 -> 拷贝；仅缺省 deleteCount -> 删到末尾。
-    let delete_count = if args.len() <= 1 {
-        0
-    } else if args.len() == 2 {
-        n - actual_start
-    } else {
-        let dc = match vm.coerce_number_bounded(vm.reg(args[2])) {
-            Ok(v) => v,
-            Err(msg) => return NativeResult::Err(from_engine_error(vm, &msg)),
-        };
-        let dc = if dc.is_nan() || dc <= 0.0 { 0 } else { dc.trunc() as usize };
-        dc.min(n - actual_start)
-    };
-    let insert_count = if args.len() > 3 { args.len() - 3 } else { 0 };
-    // ???newLen = len + insertCount - actualDeleteCount?> 2**53-1 ? TypeError?
-    // ArrayCreate(newLen) ? 2**32-1 ? RangeError??????/???????
-    let new_len = n.saturating_add(insert_count).saturating_sub(delete_count);
-    if new_len > 9_007_199_254_740_991 {
-        return NativeResult::Err(crate::error::create_type_error(vm, "Invalid array length"));
-    }
-    if let Err(err) = check_array_create_len(vm, new_len) {
-        return NativeResult::Err(err);
-    }
-    let mut out: Vec<JsValue> = Vec::with_capacity(new_len);
-    out.extend(
-        match (0..actual_start)
-            .map(|i| arraylike_get(vm, arr_ptr, i))
-            .collect::<Result<Vec<JsValue>, JsValue>>()
-        {
-            Ok(v) => v,
-            Err(err) => return NativeResult::Err(err),
-        },
-    );
-    for k in 0..insert_count {
-        out.push(vm.reg(args[3 + k]));
-    }
-    out.extend(
-        match (actual_start + delete_count..n)
-            .map(|i| arraylike_get(vm, arr_ptr, i))
-            .collect::<Result<Vec<JsValue>, JsValue>>()
-        {
-            Ok(v) => v,
-            Err(err) => return NativeResult::Err(err),
-        },
-    );
-    let new_arr = create_new_array(vm, out.len());
-    for (i, &v) in out.iter().enumerate() {
-        unsafe {
-            (*new_arr).set_prop_at(i, v);
-        }
-    }
-    NativeResult::Ok(JsValue::from_js_object(new_arr))
-}
+mod immutable;
+pub use immutable::*;