fix: set request header if not set

source/data/datasource/server/restapi.mjs

@@ -66,7 +66,7 @@ class RestAPI extends Server {
      * @property {Object} write={} Options
      * @property {Object} write.init={} An option object, containing any custom settings that you want to apply to the request. The parameters are identical to those of the {@link https://developer.mozilla.org/en-US/docs/Web/API/Request/Request|Request constructor}
      * @property {string} write.init.method=POST
-	 * @property {Object} write.init.headers Object containing any custom headers that you want to apply to the request.
+     * @property {Headers} write.init.headers Object containing any custom headers that you want to apply to the request.
      * @property {string} write.responseCallback Callback function to be executed after the request has been completed.
      * @property {string} write.acceptedStatus=[200,201]
      * @property {string} write.url URL
@@ -141,13 +141,14 @@ class RestAPI extends Server {
     read() {
         let init = this.getOption("read.init");
         if (!isObject(init)) init = {};
-		if (!init["method"]) init["method"] = "GET";
-		if (typeof init["headers"] !== "object") {
-			init["headers"] = {
-				"Accept": "application/json",
-			};
+        if (!(init["headers"] instanceof Headers)) {
+            init["headers"] = new Headers();
+            init["headers"].append("Accept", "application/json");
+            init["headers"].append("X-Requested-With", "XMLHttpRequest");
         }
 
+        if (!init["method"]) init["method"] = "GET";
+
         let callback = this.getOption("read.responseCallback");
         if (!callback) {
             callback = (obj) => {
@@ -165,11 +166,10 @@ class RestAPI extends Server {
     write() {
         let init = this.getOption("write.init");
         if (!isObject(init)) init = {};
-		if (typeof init["headers"] !== "object") {
-			init["headers"] = {
-				"Content-Type": "application/json",
-				"Accept": "application/json",
-			};
+        if (!(init["headers"] instanceof Headers)) {
+            init["headers"] = new Headers();
+            init["headers"].append("Accept", "application/json");
+            init["headers"].append("Content-Type", "application/json");
         }
         if (!init["method"]) init["method"] = "POST";