node_modules/domutils/lib/helpers.js

// removeSubsets
// Given an array of nodes, remove any member that is contained by another.
exports.removeSubsets = function(nodes) {
	var idx = nodes.length, node, ancestor, replace;

	// Check if each node (or one of its ancestors) is already contained in the
	// array.
	while (--idx > -1) {
		node = ancestor = nodes[idx];

		// Temporarily remove the node under consideration
		nodes[idx] = null;
		replace = true;

		while (ancestor) {
			if (nodes.indexOf(ancestor) > -1) {
				replace = false;
				nodes.splice(idx, 1);
				break;
			}
			ancestor = ancestor.parent;
		}

		// If the node has been found to be unique, re-insert it.
		if (replace) {
			nodes[idx] = node;
		}
	}

	return nodes;
};

// Source: http://dom.spec.whatwg.org/#dom-node-comparedocumentposition
var POSITION = {
	DISCONNECTED: 1,
	PRECEDING: 2,
	FOLLOWING: 4,
	CONTAINS: 8,
	CONTAINED_BY: 16
};

// Compare the position of one node against another node in any other document.
// The return value is a bitmask with the following values:
//
// document order:
// > There is an ordering, document order, defined on all the nodes in the
// > document corresponding to the order in which the first character of the
// > XML representation of each node occurs in the XML representation of the
// > document after expansion of general entities. Thus, the document element
// > node will be the first node. Element nodes occur before their children.
// > Thus, document order orders element nodes in order of the occurrence of
// > their start-tag in the XML (after expansion of entities). The attribute
// > nodes of an element occur after the element and before its children. The
// > relative order of attribute nodes is implementation-dependent./
// Source:
// http://www.w3.org/TR/DOM-Level-3-Core/glossary.html#dt-document-order
//
// @argument {Node} nodaA The first node to use in the comparison
// @argument {Node} nodeB The second node to use in the comparison
//
// @return {Number} A bitmask describing the input nodes' relative position.
//         See http://dom.spec.whatwg.org/#dom-node-comparedocumentposition for
//         a description of these values.
var comparePos = exports.compareDocumentPosition = function(nodeA, nodeB) {
	var aParents = [];
	var bParents = [];
	var current, sharedParent, siblings, aSibling, bSibling, idx;

	if (nodeA === nodeB) {
		return 0;
	}

	current = nodeA;
	while (current) {
		aParents.unshift(current);
		current = current.parent;
	}
	current = nodeB;
	while (current) {
		bParents.unshift(current);
		current = current.parent;
	}

	idx = 0;
	while (aParents[idx] === bParents[idx]) {
		idx++;
	}

	if (idx === 0) {
		return POSITION.DISCONNECTED;
	}

	sharedParent = aParents[idx - 1];
	siblings = sharedParent.children;
	aSibling = aParents[idx];
	bSibling = bParents[idx];

	if (siblings.indexOf(aSibling) > siblings.indexOf(bSibling)) {
		if (sharedParent === nodeB) {
			return POSITION.FOLLOWING | POSITION.CONTAINED_BY;
		}
		return POSITION.FOLLOWING;
	} else {
		if (sharedParent === nodeA) {
			return POSITION.PRECEDING | POSITION.CONTAINS;
		}
		return POSITION.PRECEDING;
	}
};

// Sort an array of nodes based on their relative position in the document and
// remove any duplicate nodes. If the array contains nodes that do not belong
// to the same document, sort order is unspecified.
//
// @argument {Array} nodes Array of DOM nodes
//
// @returns {Array} collection of unique nodes, sorted in document order
exports.uniqueSort = function(nodes) {
	var idx = nodes.length, node, position;

	nodes = nodes.slice();

	while (--idx > -1) {
		node = nodes[idx];
		position = nodes.indexOf(node);
		if (position > -1 && position < idx) {
			nodes.splice(idx, 1);
		}
	}
	nodes.sort(function(a, b) {
		var relative = comparePos(a, b);
		if (relative & POSITION.PRECEDING) {
			return -1;
		} else if (relative & POSITION.FOLLOWING) {
			return 1;
		}
		return 0;
	});

	return nodes;
};