Function compare

lib/assets/react-source/development/react.js:3117–3121

(a, b)

	}

	function compare(a, b) {
	  // Compare sort index first, then task id.
	  var diff = a.sortIndex - b.sortIndex;
	  return diff !== 0 ? diff : a.id - b.id;
	}

	// TODO: Use symbols?
	var NoPriority = 0;