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JavaScript Long Task Or Browser Freeze Detection Configuration


Germain UX RUM JS captures Javascript Long Task that occupies the UI main thread for 3 seconds or more. Usually that blocking and uninterrupted task causes:

  • Bad animations and scrolling

  • Browser Freeze

  • Delayed time to interactive (TTI)

  • High input and event handling latency

By default, this monitoring is enabled for each User Monitoring Profile.

What the Chrome team says about Javascript Long Task:



You can update long task threshold by setting settings.plugins.performance.longtaskThresholdMillis in the Init Script.

The following code sample shows how to collect long tasks only if equal or longer than five seconds.

const settings = germainApm.getDefaultSettings();
settings.plugins.performance.longtaskThresholdMillis = 5000; // in milliseconds


  • KPI Name: “Javascript Long Task - Browser Freeze”. More details.


Long Tasks on Drill-through

Javascript Long Task - Browser Freeze on Drill-through

Javascript Long Task - Browser Freeze on Replay of User Session dashboard - Germain UX

Component: RUM JS

Feature Availability: 2022.2 or later

Browser Support: only latest Chrome, Edge and Opera

JavaScript errors detected

Please note, these errors can depend on your browser setup.

If this problem persists, please contact our support.