🩹 fix(api): Correctly handle undefined breakTies.

Author: make-github-pseudonymous-again

README.md

@@ -14,7 +14,10 @@ sorted(["ab", "bc"]); // abc
 
 // Add a comparison function to break ties.
 import {increasing} from '@aureooms/js-compare';
-sorted(["ab", "cd"], increasing); // acbd
+sorted(["ab", "cd"], increasing); // abcd
+
+import {decreasing} from '@aureooms/js-compare';
+sorted(["ab", "cd"], decreasing); // cdab
 ```
 
 [![License](https://img.shields.io/github/license/aureooms/js-topological-sorting.svg)](https://raw.githubusercontent.com/aureooms/js-topological-sorting/main/LICENSE)

src/sorted.js

@@ -10,10 +10,10 @@ import kahn from './kahn.js';
  * @param {(a: any, b: any) => Number} breakTies - The function to break ties.
  * @returns {Iterable<any>} The vertices sorted in topological order.
  */
-export default function sorted(edges, breakTies = (_a, _b) => -1) {
+export default function sorted(edges, breakTies = undefined) {
 	const graph = Pairs.from(edges);
 
-	const queue = new Heap(breakTies);
+	const queue = breakTies ? new Heap(breakTies) : [];
 	const freeVertices = new Set();
 	for (const [u] of graph) freeVertices.add(u);
 	for (const [, v] of graph) freeVertices.delete(v);

test/src/api.js

@@ -124,3 +124,21 @@ test('Triangle after edge', (t) => {
 	const edges = ['xa', 'ab', 'bc', 'ca'];
 	t.throws(() => [...sorted(edges)], {message: /cycle/});
 });
+
+test('README example #1', (t) => {
+	const edges = ['ab', 'bc'];
+	const expected = ['a', 'b', 'c'];
+	t.deepEqual([...sorted(edges)], expected);
+});
+
+test('README example #2', (t) => {
+	const edges = ['ab', 'cd'];
+	const expected = ['a', 'b', 'c', 'd'];
+	t.deepEqual([...sorted(edges, increasing)], expected);
+});
+
+test('README example #3', (t) => {
+	const edges = ['ab', 'cd'];
+	const expected = ['c', 'd', 'a', 'b'];
+	t.deepEqual([...sorted(edges, decreasing)], expected);
+});