diff --git a/__wasm/wit-bindgen-sample/container/src/main.rs b/__wasm/wit-bindgen-sample/container/src/main.rs
index b58295f..029bad9 100644
--- a/__wasm/wit-bindgen-sample/container/src/main.rs
+++ b/__wasm/wit-bindgen-sample/container/src/main.rs
@@ -1,4 +1,5 @@
 use std::time::Duration;
+
 use anyhow::Result;
 use serde::{Deserialize, Serialize};
 use wasmtime::{Config, Engine, Instance, Linker, Module, Store};
@@ -11,11 +12,23 @@ struct FetchResult {
     result: Option<String>,
 }
 
+impl FetchResult {
+    fn to_json(&self) -> String {
+        serde_json::to_string(&self).expect("JSResult to json error")
+    }
+}
+
 #[derive(Clone, Debug, Serialize, Deserialize)]
 struct JsResult {
     message: String,
 }
 
+impl JsResult {
+    fn to_json(&self) -> String {
+        serde_json::to_string(&self).expect("JSResult to json error")
+    }
+}
+
 pub fn get(url: &str) -> reqwest::Result<reqwest::blocking::Response> {
     let client = reqwest::blocking::Client::builder()
         .timeout(Duration::from_secs(8))
@@ -36,21 +49,21 @@ impl container::Container for MyContainer {
         let url: String = s.chars().skip(1).take(s.len() - 2).collect();
         println!("fetch arguments URL: {}", url);
         let r = match get(&url) {
-            Err(e) => return serde_json::to_string(&FetchResult {
-                error: Some(serde_json::to_string(&JsResult {
+            Err(e) => return FetchResult {
+                error: Some(JsResult {
                     message: format!("failed: {}", e)
-                }).expect("to json failed.4")),
+                }.to_json()),
                 result: None,
-            }).expect("to json failed.3"),
+            }.to_json(),
             Ok(r) => r,
         };
 
-        serde_json::to_string(&FetchResult {
+        FetchResult {
             error: None,
-            result: Some(serde_json::to_string(&JsResult {
+            result: Some(JsResult {
                 message: format!("fetched: {:?}", r.text()),
-            }).expect("to json failed.1")),
-        }).expect("to json failed.2")
+            }.to_json()),
+        }.to_json()
     }
 }