JavaScript Beacon Guide
sendBeacon reliably sends data to the server even after page close. Ideal for analytics and diagnostics. The guide walks through Sending Beacons. `navigator.sendBeacon(url,data)` — POST request, returns true if queued. Data: string, FormData, Blob. Use in `beforeunload` — unlike fetch, beacon completes after page closes. reliable, async, fire-and-forget. Use for: analytics events, session end logging, crash reports. The guide is organized into 1 sections that build on each other, each pairing a prose explanation with runnable code. Related guides: Arrays, Strings, Numbers, Math, Date. This is one of 145 JavaScript guides on JS Reference — see the full list on the guides page. Practice what you learn in the JavaScript playground, and look up any unfamiliar term in the JavaScript glossary.