diff --git a/javascript-container/src/main.rs b/javascript-container/src/main.rs
index c5937a1..35f9010 100644
--- a/javascript-container/src/main.rs
+++ b/javascript-container/src/main.rs
@@ -15,8 +15,8 @@ fn main() -> Result<()> {
 
     let memory = instance.get_memory(&mut store, "memory").expect("SHOULD NOT HAPPEN");
     let malloc = instance.get_typed_func::<i32, i32>(&mut store, "malloc")?;
-    let free = instance.get_typed_func::<(i32, i32), ()>(&mut store, "free")?;
-    let eval = instance.get_typed_func::<(i32, i32), (i32, i32)>(&mut store, "eval")?;
+    let free = instance.get_typed_func::<i32, ()>(&mut store, "free")?;
+    let eval = instance.get_typed_func::<i32, i32>(&mut store, "eval")?;
 
     let js = "1+2";
     let js_bytes = js.as_bytes();
@@ -24,10 +24,26 @@ fn main() -> Result<()> {
     let ptr = malloc.call(&mut store, js.as_bytes().len() as i32)?;
     let memory_data_mut = memory.data_mut(&mut store);
     for i in 0..js_bytes_len {
-        memory_data_mut[ptr as usize + i] = js_bytes[i];
+        memory_data_mut[4 + ptr as usize + i] = js_bytes[i];
     }
-    let eval_result = eval.call(&mut store, (ptr, js_bytes_len as i32))?;
+    let eval_result = eval.call(&mut store, ptr)?;
     println!("Eval result: {:?}", eval_result);
 
+    let memory = instance.get_memory(&mut store, "memory").expect("SHOULD NOT HAPPEN");
+    let memory_data_mut = memory.data_mut(&mut store);
+    let mut a = [0_u8; 4];
+    a[0] = memory_data_mut[eval_result as usize + 0];
+    a[1] = memory_data_mut[eval_result as usize + 1];
+    a[2] = memory_data_mut[eval_result as usize + 2];
+    a[3] = memory_data_mut[eval_result as usize + 3];
+    let aa = u32::from_be_bytes(a);
+    println!("Len: {}", aa);
+    let mut s = Vec::with_capacity(aa as usize);
+    for i in 0..aa {
+        s.push(memory_data_mut[eval_result as usize + 4 + i as usize]);
+    }
+    let ss = unsafe { String::from_utf8_unchecked(s) };
+    println!("Result: {}", ss);
+
     Ok(())
 }
diff --git a/javascript-engine/src/lib.rs b/javascript-engine/src/lib.rs
index b6cc094..7fa7eeb 100644
--- a/javascript-engine/src/lib.rs
+++ b/javascript-engine/src/lib.rs
@@ -2,10 +2,10 @@ mod mem;
 mod engine;
 
 #[no_mangle]
-pub unsafe fn eval(ptr: *mut u8, len: usize) -> (*mut u8, usize) {
-    let js = mem::read_string(ptr, len);
+pub unsafe fn eval(ptr: *mut u8) -> *mut u8 {
+    let js = mem::read_string(ptr);
     let eval_result = engine::inner_eval(&js);
     let eval_result_json_string = serde_json::to_string(&eval_result).expect("SHOULD NOT HAPPEN");
-    mem::malloc_and_write_string(&eval_result_json_string)
+    mem::malloc_and_write_string(&eval_result_json_string).0
 }
 
diff --git a/javascript-engine/src/mem.rs b/javascript-engine/src/mem.rs
index 2e88bbe..2b6a970 100644
--- a/javascript-engine/src/mem.rs
+++ b/javascript-engine/src/mem.rs
@@ -3,23 +3,24 @@ use std::ptr;
 #[no_mangle]
 pub unsafe fn malloc(len: usize) -> *mut u8 {
     let align = std::mem::align_of::<usize>();
-    let layout = std::alloc::Layout::from_size_align_unchecked(len, align);
-    std::alloc::alloc(layout)
+    let layout = std::alloc::Layout::from_size_align_unchecked(len + 4, align);
+    let addr = std::alloc::alloc(layout);
+    let len_in_bytes = (len as u32).to_be_bytes();
+    write_bytes(addr, 0, 4, &len_in_bytes);
+    addr
 }
 
 #[no_mangle]
-pub unsafe fn free(ptr: *mut u8, len: usize) {
+pub unsafe fn free(ptr: *mut u8) {
+    let len = read_u32(ptr);
     let align = std::mem::align_of::<usize>();
-    let layout = std::alloc::Layout::from_size_align_unchecked(len, align);
+    let layout = std::alloc::Layout::from_size_align_unchecked(4 + len as usize, align);
     std::alloc::dealloc(ptr, layout)
 }
 
-pub(crate) fn read_string(ptr: *const u8, len: usize) -> String {
-    let mut buffer = Vec::with_capacity(len);
-    let len = len as isize;
-    for i in 0..len {
-        buffer.push(unsafe { ptr::read(ptr.offset(i)) });
-    }
+pub(crate) fn read_string(ptr: *const u8) -> String {
+    let len = read_u32(ptr);
+    let buffer = read_bytes(ptr, 4, len as usize);
     unsafe { String::from_utf8_unchecked(buffer) }
 }
 
@@ -27,14 +28,32 @@ pub(crate) unsafe fn malloc_and_write_string(str: &str) -> (*mut u8, usize) {
     let bytes = str.as_bytes();
     let bytes_len = bytes.len();
     let ptr = malloc(bytes_len);
-    write_bytes(ptr, bytes_len, bytes);
+    write_bytes(ptr, 4, bytes_len, bytes);
     (ptr, bytes_len)
 }
 
-pub(crate) fn write_bytes(ptr: *mut u8, len: usize, bytes: &[u8]) {
+pub(crate) fn read_u32(ptr: *const u8) -> u32 {
+    let vec_u32 = read_bytes(ptr, 0, 4);
+    let mut bytes_u32 = [0_u8; 4];
+    bytes_u32[0] = vec_u32[0];
+    bytes_u32[1] = vec_u32[1];
+    bytes_u32[2] = vec_u32[2];
+    bytes_u32[3] = vec_u32[3];
+    u32::from_be_bytes(bytes_u32)
+}
+
+pub(crate) fn read_bytes(ptr: *const u8, offset: isize, len: usize) -> Vec<u8> {
+    let mut buffer = Vec::with_capacity(len);
+    for i in 0..len {
+        buffer.push(unsafe { ptr::read(ptr.offset(offset + i as isize)) });
+    }
+    buffer
+}
+
+pub(crate) fn write_bytes(ptr: *mut u8, offset: isize, len: usize, bytes: &[u8]) {
     let bytes_len = bytes.len();
     assert!(bytes_len <= len);
     for i in 0..bytes_len {
-        unsafe { ptr::write(ptr.offset(i as isize), bytes[i]) };
+        unsafe { ptr::write(ptr.offset(offset + i as isize), bytes[i]) };
     }
 }