JavaScript errors

The javascript-errors command counts browser errors by page and message. It includes uncaught exceptions and unhandled promise rejections.

Add the optional rollup to your scheduled questions:

import { javascriptErrors, rollups } from "@kensio/rainlytics";

new RollupSummaries(this, "Summaries", {
  table,
  workgroup,
  rollups: [...rollups, javascriptErrors],
});

rainlytics javascript-errors --last 24h

page       message                                           errors
---------  ------------------------------------------------  ------
/checkout  TypeError: Cannot read properties of undefined        27
/account   Error: Session expired                                 9

Enable collection

Import error reporting in the measured site:

import { startBeacon } from "@kensio/rainlytics/beacon";
import { reportErrors } from "@kensio/rainlytics/beacon/errors";

const beacon = startBeacon();
reportErrors(beacon);

error events come from uncaught exceptions. rejection events come from unhandled promise rejections. The browser’s normal error behavior is unchanged.

The rollup is optional because a site without browser error events would pay for an empty query on every scheduled window. Adding it under the default schedule adds 50 Athena queries a day.

Grouping and redaction

Rows group by the exact page and message sent by the browser. Error and rejection events with the same page and message share one row. If a message includes a different order ID on each request, each ID produces a separate row.

Normalize a message before sending when several values should form one group:

reportErrors(beacon, {
  redact: (message) => message.replace(/Order \d+/gu, "Order [number]"),
});

This also protects the raw log. A query-time replacement changes the report but leaves the original message in S3.

Error messages can contain personal data. Review every message your application can produce and use redact before enabling collection. Messages are limited to 200 characters and stack traces are never sent.

Custom collection paths

The rollup reads the default /_rainlytics path. Record another path in its summary request:

new RollupSummaries(this, "Summaries", {
  table,
  workgroup,
  rollups: [...rollups, javascriptErrors],
  requests: {
    "javascript-errors": { paths: ["/_measure"] },
  },
});

Use the same path with BeaconPath and startBeacon.

Combined windows

The command adds counts for matching page and message pairs across stored windows. Each summary stores only its highest-ranked rows, so the combined ranking may omit errors that were below the limit in individual windows. Add --query to rank all raw events across the full range.