Merge pull request #42172 from ramthi/patch-3

Update api-filtering-sampling.md

articles/azure-monitor/app/api-filtering-sampling.md

@@ -21,11 +21,11 @@ You can write and configure plug-ins for the Application Insights SDK to customi
 
 Before you start:
 
-* Install the appropriate SDK for your application: [ASP.NET](asp-net.md), [ASP.NET Core](asp-net-core.md), [Non HTTP/Worker for .NET/.NET Core](worker-service.md), or [Java](../../azure-monitor/app/java-get-started.md).
+* Install the appropriate SDK for your application: [ASP.NET](asp-net.md), [ASP.NET Core](asp-net-core.md), [Non HTTP/Worker for .NET/.NET Core](worker-service.md), [Java](../../azure-monitor/app/java-get-started.md) or [JavaScript](javascript.md)
 
 <a name="filtering"></a>
 
-## Filtering: ITelemetryProcessor
+## Filtering
 
 This technique gives you direct control over what is included or excluded from the telemetry stream. Filtering can be used to drop telemetry items from being sent to Application Insights. You can use it in conjunction with Sampling, or separately.
 
@@ -195,7 +195,30 @@ public void Process(ITelemetry item)
 
 <a name="add-properties"></a>
 
-## Add properties: ITelemetryInitializer
+### JavaScript Web applications
+
+**Filtering using ITelemetryInitializer**
+
+1. Create a telemetry initializer callback function. The callback function takes `ITelemetryItem` as a parameter, which is the event that is being processed. Returning `false` from this callback results in the telemetry item to be filtered out.  
+
+   ```JS
+   var filteringFunction = (envelope) => {
+     if (envelope.data.someField === 'tobefilteredout') {
+     	return false;
+     }
+
+     return true;
+   };
+   ```
+
+2. Add your telemetry initializer callback:
+
+   ```JS
+   appInsights.addTelemetryInitializer(filteringFunction);
+   ```
+
+## Add/modify properties: ITelemetryInitializer
+
 
 Use telemetry initializers to enrich telemetry with additional information and/or to override telemetry properties set by the standard telemetry modules.