The browser you targeting need to have support of WeakMap and String.prototype.includes. If you need to support an older browser (like IE) you will need to include polyfill for WeakMap and String.prototype.includes (see https://github.com/zloirock/core-js for example).
If you want to use IntersectionObserver and want to target Safari and/or IE; you need to include a polyfill.
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