arraydiff.js

//leaves only the unique elements in two sorted arrays
function diff(bob, steve) {
	for (let b = 0, s = 0; b < bob.length && s < steve.length; ++b, ++s) {
		if (bob[b] < steve[s])
			--s;
		else if (bob[b] > steve[s])
			--b;
		else {
			bob.splice(b--, 1);
			steve.splice(s--, 1);
		}
	}
}

arrayindex.js

//gets the index an element would belong in a sorted array
function (
	arr,
	el,
	prefer = (prefer, against) => (
		(prefer == against) ? null : prefer < against
	)
) {
	let index = 0;
	for (
		let top = arr.length, preference, test;
		index < top;
		(preference !== false) && (top = test),
		(preference !== true) && (index = test + 1)
	)
		preference = prefer(el, arr[test = (index + top) >>> 1]);
	return index;
}