src/concat.js
function saveSlot(aList, bList, index, slot) {
	setEither(aList, bList, index, slot);

	var isInFirst = (index === 0 || index === aList.sizes.length);
	var len = isInFirst ? 0 : getEither(aList.sizes, bList.sizes, index - 1);

	setEither(aList.sizes, bList.sizes, index, len + length(slot));
}
function saveSlot(aList, bList, index, slot) {
	setEither(aList, bList, index, slot);

	var isInFirst = (index === 0 || index === aList.sizes.length);
	var len = isInFirst ? 0 : getEither(aList.sizes, bList.sizes, index - 1);

	setEither(aList.sizes, bList.sizes, index, len + length(slot));
}
function saveSlot ( aList , bList , index , slot ) { setEither ( aList , bList , index , slot ) ; var isInFirst = ( index === 0 || index === aList . sizes . length ) ; var len = isInFirst ? 0 : getEither ( aList . sizes , bList . sizes , index - 1 ) ; setEither ( aList . sizes , bList . sizes , index , len + length ( slot ) ) ; }
helper for setting picking a slot between to nodes
@param {Node} aList - a non-leaf node
@param {Node} bList - a non-leaf node
@param {number} index
@param {Node} slot
helper for setting picking a slot between to nodes