Intervention Reporting Demo

Intervention reporting active — the browser will report when it overrides your code

What is an intervention?

An intervention is when the browser silently ignores or changes your code's behaviour to protect users

Note: Browser support for routing intervention reports through the Reporting API is inconsistent. Chrome may log the intervention to the console rather than sending it as a report. The Reporting-Endpoints header is still sent with this page — reports will be delivered if and when the browser chooses to send them.

The classic example is calling preventDefault() inside a passive event listener. Browsers mark wheel and touchstart listeners as passive by default to keep scrolling smooth. If your code calls preventDefault() inside one, the browser ignores the call — and may generate an intervention report. You can see the intervention happening in the browser console: Unable to preventDefault inside passive event listener invocation.

Reporting-Endpoints header sent with this page

Reporting-Endpoints: default="https://helios.report-uri.com/a/t/g"

How intervention reporting works

When the browser overrides your code it can generate an intervention report and deliver it asynchronously to your Reporting-Endpoints endpoint. This gives you visibility into places where the browser is silently changing how your code behaves in production — across real user sessions — so you can fix the underlying issue rather than discovering it through user complaints or performance regressions.

Example intervention report payload (sent by the browser)

[{
  "age": 0,
  "type": "intervention",
  "url": "https://report-uri-demo.com/intervention/",
  "body": {
    "id": "PreventDefaultPassiveListener",
    "message": "Unable to preventDefault inside passive event listener invocation.",
    "sourceFile": "https://report-uri-demo.com/intervention/",
    "lineNumber": 42,
    "columnNumber": 7
  }
}]