Spread operators in object literals cause crashes in Edge/EdgeHTML

Bug Report

naja built source contains spread operator (...) in object literals, which is ES2018 feature. But Edge 12-18 (with EdgeHTML core) throws syntax error, because they implement only ES2015.

In the migration guide from v1 to v2, there is only mentioned that IE is no more supported, no mention about Edge. But .browserslistrc list last 2 versions which mean that old Edges with EdgeHTML core do not match anymore.

[jiripudil]

I mean, you can always tweak your build configuration to further transpile naja if you need to support any ancient browser (Edge 16 is almost 3 years old). It just doesn’t make sense to me for Naja itself to support anything else than the latest version.

[dakur]

I’ve created this patch for myself quickly and found no further problem in Edge 18.

diff --git a/node_modules/naja/dist/Naja.esm.js b/node_modules/naja/dist/Naja.esm.js
index bd4b5c5..e61823c 100644
--- a/node_modules/naja/dist/Naja.esm.js
+++ b/node_modules/naja/dist/Naja.esm.js
@@ -1172,12 +1172,8 @@ class Naja extends EventTarget {
       url = url.href;
     }
 
-    options = { ...this.defaultOptions,
-      ...options,
-      fetch: { ...(this.defaultOptions.fetch || {}),
-        ...(options.fetch || {})
-      }
-    };
+    const fetchOptions = Object.assign({}, this.defaultOptions.fetch || {}, options.fetch || {});
+    options = Object.assign({}, this.defaultOptions, options, {fetch: fetchOptions});
 
     if (method.toUpperCase() === 'GET' && data instanceof FormData) {
       const urlObject = new URL(url, location.href);
@@ -1191,14 +1187,15 @@ class Naja extends EventTarget {
     }
 
     const abortController = new AbortController();
-    const request = new Request(url, {
-      credentials: 'same-origin',
-      ...options.fetch,
-      method,
-      headers: new Headers(options.fetch.headers || {}),
-      body: data !== null && Object.getPrototypeOf(data) === Object.prototype ? new URLSearchParams(data) : data,
-      signal: abortController.signal
-    }); // impersonate XHR so that Nette can detect isAjax()
+
+    const requestOptions = Object.assign({}, {
+		credentials: 'same-origin',
+		method,
+		headers: new Headers(options.fetch.headers || {}),
+		body: data !== null && Object.getPrototypeOf(data) === Object.prototype ? new URLSearchParams(data) : data,
+		signal: abortController.signal
+	}, options.fetch);
+    const request = new Request(url, requestOptions);
 
     request.headers.set('X-Requested-With', 'XMLHttpRequest');