Checking readyState is interactive before listening for DOMContentLoaded

[andrew-ebsco]

Description

This is to fix issue #2264. Sometimes DOMContentLoaded can fire before readyState === 'complete'.

Corresponding issue:

Testing

The unit test suite passed.

Checklist

• [x] I have read the contribution guidelines
• [x] I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• [x] This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• [x] I ran the test suite locally (npm run test) and verified that it succeeded