There are some disagreements between python and javascript code styles. scored_on_percent, scored_on_end are data from backend and names of fields on backend.
From my side I do  [conversions](https://github.com/edx/edx-platform/blob/anton/video-player-grading/common/lib/xmodule/xmodule/js/src/video/10_grader_collection.js#L22) here and use camel case style for naming of js graders.