This metric measures, for each file, how often it uses language features that were introduced in ECMAScript 2015 (also known as ECMAScript 6) or later.

If a code base is intended to be ECMAScript 5 compatible, this metric can be used to identify parts of the code base that are making use of new features that are not yet available in ECMAScript 5.

For code bases that should be migrated to ECMAScript 2015 or later, tracking this metric over time is useful for assessing the progress of the migration.

Ecma International: ECMAScript 2015 Language Specification.