feat(js): Add documentation for setSpanActive(span: Span)

Author: Lms24

docs/platforms/javascript/common/apis.mdx

@@ -636,6 +636,51 @@ See <PlatformLink to="/tracing/instrumentation/">Tracing Instrumentation</Platfo
 
 </SdkApi>
 
+<SdkApi
+ name="setSpanActive"
+ signature="function setSpanActive(span: Span): void"
+ availableSince="10.14.0"
+ categorySupported={["browser"]}
+ parameters={[
+  {
+    name: "span",
+    required: true,
+    type: "Span",
+    description: "The span to be set active"
+  }
+ ]}
+ >
+  Sets the passed span as the active span on the current scope.
+  You most likely don't need this functionality but should [use `startActiveSpan`](#startActiveSpan) 
+  instead.
+  However, in some situations, you might prefer a span being active outside of a callback. 
+  In this case, the combination of [`startInactiveSpan`](#startInactiveSpan) with this function
+  allows you to start a span, hold a reference to it and keep it active until you end it, without
+  the active duration being bound to the callback (as opposed to [`startSpanManual`](#startSpanManual)).
+  
+  
+  <Expandable title='Examples'>
+  ```javascript
+  let checkoutSpan;
+  
+  on('startCheckout', () => {
+    checkoutSpan = Sentry.startInactiveSpan({name: 'checkout-flow'});
+    Sentry.setSpanActive(checkoutSpan);
+  })
+  
+  doSomeWork();
+  
+  on('endCheckout', () => {
+    // Ending the span automatically removes it as the active span on the scope
+    checkoutSpan.end();
+  })
+  ```
+</Expandable>
+
+See <PlatformLink to="/tracing/instrumentation/">Tracing Instrumentation</PlatformLink> for more information on how to work with spans.
+
+</SdkApi>
+
 <SdkApi
   name="continueTrace"
   signature="function continueTrace<T>(options: TraceOptions, callback: () => T): T"

docs/platforms/javascript/common/tracing/instrumentation/index.mdx

@@ -102,8 +102,33 @@ Sometimes, you do not want the span to be ended automatically when the callback
 
 To add spans that aren't active, you can create independent spans. This is useful when you have work that is grouped together under a single parent span, but is independent from the currently active span. However, in most cases you'll want to create and use the [startSpan](#starting-an-active-span-startspan) API from above.
 
+
 <PlatformContent includePath="performance/start-inactive-span" />
 
+<PlatformCategorySection supported={['browser']}>
+
+  In some cases, you may need to start an inactive span and make it the active span.
+  In contrast to [startSpanManual](#starting-an-active-span-with-manual-end-startspanmanual), the period for which 
+  the span is active is not bound to the callback. Instead, it will remain active until you manually end the span.
+
+  ```javascript
+  let checkoutSpan;
+  
+  on('startCheckout', () => {
+    checkoutSpan = Sentry.startInactiveSpan({name: 'checkout-flow'});
+    Sentry.setSpanActive(checkoutSpan);
+  })
+  
+  doSomeWork();
+  
+  on('endCheckout', () => {
+    // Ending the span automatically removes it as the active span on the scope
+    checkoutSpan.end();
+  })
+  ```
+
+</PlatformCategorySection>
+
 ## Starting Spans as Children of a Specific Span
 
 By default, any span that is started will be the child of the currently active span. If you want to have a different behavior, you can force spans to be the children of a specific span with the `parentSpan` option: