This script builds on top of the original work done in #121 with the following changes:

• Adds support for the rootMargin property
• Adds logic to account for parent elements with non-visible overflow
• Adds support for elements on a delayed intersection (e.g. CSS transitions)
• Adds detection of elements on the boundary
• Adds detection of zero-sized elements within root's bounds
• Updates to support targets and roots being added/removed from the DOM
• Removes newer ES6 constructs (like Map) for broader support

With these changes, this polyfill test suite passes in native implementations (Chrome 52+), the latest version of all major browsers, and IE back to version 8 (I didn't test 6-7, but they may work as well).

TODO:

This version uses polling on a 100ms timeout to get the greatest legacy support. I plan to add new logic to use a combination of scroll, resize, and MutationObserver listeners + temporary polling to detect CSS transitions soon, but I wanted to start the pull request with my initial set of changes so we could discuss.

/cc @surma @ojanvafai @triblondon