Check if browser supports keepalive for network requests (#90)

src/StatsigLogger.ts

@@ -19,11 +19,6 @@ type FailedLogEventBody = {
   time: number;
 };
 
-let SUPPORTS_KEEPALIVE = false;
-try {
-  SUPPORTS_KEEPALIVE = 'keepalive' in new Request('');
-} catch (_e) {}
-
 const MS_RETRY_LOGS_CUTOFF = 5 * 24 * 60 * 60 * 1000;
 
 export default class StatsigLogger {
@@ -133,7 +128,7 @@ export default class StatsigLogger {
 
     const oldQueue = this.queue;
     this.queue = [];
-    if (isClosing && !SUPPORTS_KEEPALIVE && navigator && navigator.sendBeacon) {
+    if (isClosing && !this.sdkInternal.getNetwork().supportsKeepalive() && navigator && navigator.sendBeacon) {
       const beacon = this.sdkInternal.getNetwork().sendLogBeacon({
         events: oldQueue,
         statsigMetadata: this.sdkInternal.getStatsigMetadata(),

src/StatsigNetwork.ts

@@ -14,9 +14,14 @@ export default class StatsigNetwork {
 
   private leakyBucket: Record<string, number>;
 
+  private canUseKeepalive : boolean = false;
+
   public constructor(sdkInternal: IHasStatsigInternal) {
     this.sdkInternal = sdkInternal;
     this.leakyBucket = {};
+    try {
+      this.canUseKeepalive = 'keepalive' in new Request('');
+    } catch (_e) {}
   }
 
   public fetchValues(
@@ -117,17 +122,20 @@ export default class StatsigNetwork {
       this.leakyBucket[url] = counter + 1;
     }
 
-    const params = {
+    const params : RequestInit = {
       method: 'POST',
       body: JSON.stringify(body),
       headers: {
         'Content-type': 'application/json; charset=UTF-8',
         'STATSIG-API-KEY': this.sdkInternal.getSDKKey(),
         'STATSIG-CLIENT-TIME': Date.now() + '',
       },
-      keepalive: true,
     };
 
+    if (this.canUseKeepalive) {
+      params.keepalive = true;
+    }
+
     return fetch(url, params)
       .then((res) => {
         if (res.ok) {
@@ -157,4 +165,8 @@ export default class StatsigNetwork {
         this.leakyBucket[url] = Math.max(this.leakyBucket[url] - 1, 0);
       });
   }
+
+  public supportsKeepalive(): boolean {
+    return this.canUseKeepalive;
+  }
 }