MooTools related errors encountered

Problem

You're using the MooTools library and notice errors like the ones below showing up in the browser console or on the JavaScript errors page.

• Uncaught TypeError: t is not a function

• Uncaught (in promise) TypeError: Failed to execute 'removeEventListener' on 'EventTarget': 2 arguments required, but only 0 present.

Cause

The MooTools library (especially its compatibility layer) mutates a number of native JavaScript objects and methods, which can cause conflicts with newer libraries, including the New Relic browser agent.

Solutions

1. Because the last version of MooTools was released in 2016, migrating from MooTools to other actively maintained libraries may be the best strategic choice when possible.

2. If migrating from MooTools is not an option, we recommend updating to a nocompat build of the latest MooTools version, 1.6.0.

3. If you use a custom build of MooTools, you may need to disable the compatibility layer when generating the custom build.