Enhance proxy fallback handling

Author: EmilianoSanchez

CHANGES.txt

@@ -1,3 +1,6 @@
+2.4.1 (June 3, 2025)
+ - Bugfix - Enhanced the Proxy fallback to flag spec version 1.2 to support some Fetch API implementations that might fail to handle Proxy 400 responses.
+
 2.4.0 (May 27, 2025)
  - Added support for rule-based segments. These segments determine membership at runtime by evaluating their configured rules against the user attributes provided to the SDK.
  - Added support for feature flag prerequisites. This allows customers to define dependency conditions between flags, which are evaluated before any allowlists or targeting rules.

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@splitsoftware/splitio-commons",
-  "version": "2.4.0",
+  "version": "2.4.1",
   "description": "Split JavaScript SDK common components",
   "main": "cjs/index.js",
   "module": "esm/index.js",

package.json

@@ -40,9 +40,9 @@ export function splitChangesFetcherFactory(fetchSplitChanges: IFetchSplitChanges
     }
 
     let splitsPromise = fetchSplitChanges(since, noCache, till, settings.sync.flagSpecVersion === FLAG_SPEC_VERSION ? rbSince : undefined)
-      // Handle proxy error with spec 1.3
       .catch((err) => {
-        if (err.statusCode === 400 && sdkEndpointOverridden(settings) && settings.sync.flagSpecVersion === FLAG_SPEC_VERSION) {
+        // Handle proxy error with spec 1.3
+        if ((!err.statusCode || err.statusCode === 400) && sdkEndpointOverridden(settings) && settings.sync.flagSpecVersion === FLAG_SPEC_VERSION) {
           log.error(LOG_PREFIX_SYNC_SPLITS + 'Proxy error detected. Retrying with spec 1.2. If you are using Split Proxy, please upgrade to latest version');
           lastProxyCheckTimestamp = Date.now();
           settings.sync.flagSpecVersion = '1.2'; // fallback to 1.2 spec