added async http request and removed old sync impl

src/main/java/com/limechain/teavm/HttpRequest.java

@@ -1,8 +1,32 @@
 package com.limechain.teavm;
 
+import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.jso.JSBody;
+import org.teavm.jso.JSFunctor;
+import org.teavm.jso.JSObject;
+import org.teavm.jso.core.JSError;
+
+import java.io.IOException;
 
 public class HttpRequest {
-    @JSBody(params = {"method", "url", "body"}, script = "return httpRequestSync(method, url, body);")
-    public static native String httpRequestSync(String method, String url, String body);
+    @JSFunctor
+    interface HttpRequestCallback extends JSObject {
+        void apply(JSError error, String response);
+    }
+
+    @Async
+    public static native String asyncHttpRequest(String method, String url, JSObject body);
+    private static void asyncHttpRequest(String method, String url, JSObject body, AsyncCallback<String> callback) {
+        createAsyncHttpRequest(method, url, body, (error, response) -> {
+            if (error != null) {
+                callback.error(new IOException(error.getMessage()));
+            } else {
+                callback.complete(response);
+            }
+        });
+    }
+
+    @JSBody(params = {"method", "url", "body", "callback"}, script = "return asyncHttpRequest(method, url, body, callback);")
+    public static native void createAsyncHttpRequest(String method, String url, JSObject body, HttpRequestCallback callback);
 }

src/main/java/com/limechain/utils/json/JsonUtil.java

@@ -13,6 +13,6 @@ public static String stringify(Object object) {
     }
 
     public static String readJsonFromFile(String filePath) {
-        return HttpRequest.httpRequestSync("GET", filePath, null);
+        return HttpRequest.asyncHttpRequest("GET", filePath, null);
     }
 }

src/main/webapp/js/http.js

@@ -1,15 +1,22 @@
-function httpRequestSync(method, url, body) {
-    var xhr = new XMLHttpRequest();
-    xhr.open(method, url, false); // false for synchronous request
-    xhr.setRequestHeader('Content-Type', 'application/json');
-    if (method === 'POST' && body) {
-        xhr.send(body);
-    } else {
-        xhr.send();
-    }
-    if (xhr.status === 200) {
-        return xhr.responseText;
-    } else {
-        throw new Error('Request failed with status ' + xhr.status);
+async function asyncHttpRequest(method = 'GET', url, body = null, callback) {
+    try {
+        const response = await fetch(url, {
+            method: method,
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: method === 'POST' ? JSON.stringify(body) : undefined
+        });
+
+        if (!response.ok) {
+            callback(new Error(`Request failed with status: ${response?.status}`), null);
+            return;
+        }
+
+        let result = await response.text();
+        callback(null, result);
+
+    } catch (error) {
+        callback(new Error(`Error during sending request: ${error.message}`), null);
     }
 }