✨ feat: Add insertAfter.

Author: make-github-pseudonymous-again

src/Node.js

@@ -2,8 +2,9 @@
  * Node.
  *
  * @param {any} value
+ * @param {Node} next
  */
-export default function Node(value) {
+export default function Node(value, next) {
 	this._value = value;
-	this._next = null;
+	this._next = next;
 }

src/_insertAfter.js

@@ -0,0 +1,19 @@
+import assert from 'assert';
+
+// eslint-disable-next-line no-unused-vars
+import Node from './Node.js';
+import isNonEmpty from './isNonEmpty.js';
+import unshift from './unshift.js';
+import _setNext from './_setNext.js';
+import _shift from './_shift.js';
+
+/**
+ * Inserts value just after input node (cannot be null).
+ *
+ * @param {Node} x Input node (cannot be null).
+ * @param {any} value
+ */
+export default function _insertAfter(x, value) {
+	assert(isNonEmpty(x));
+	_setNext(x, unshift(_shift(x), value));
+}

src/index.js

@@ -1,4 +1,5 @@
 export {default as Node} from './Node.js';
+export {default as _insertAfter} from './_insertAfter.js';
 export {default as _isLast} from './_isLast.js';
 export {default as _iter} from './_iter.js';
 export {default as _iter_fast} from './_iter_fast.js';
@@ -12,6 +13,7 @@ export {default as _value} from './_value.js';
 export {default as concat} from './concat.js';
 export {default as empty} from './empty.js';
 export {default as from} from './from.js';
+export {default as insertAfter} from './insertAfter.js';
 export {default as isEmpty} from './isEmpty.js';
 export {default as isLast} from './isLast.js';
 export {default as isList} from './isList.js';

src/insertAfter.js

@@ -0,0 +1,19 @@
+import assert from 'assert';
+
+// eslint-disable-next-line no-unused-vars
+import Node from './Node.js';
+import isNonEmpty from './isNonEmpty.js';
+import isEmpty from './isEmpty.js';
+import _insertAfter from './_insertAfter.js';
+
+/**
+ * Inserts value just after input node. Throws if input list is empty
+ *
+ * @param {Node} x Input node.
+ * @param {any} value
+ */
+export default function insertAfter(x, value) {
+	if (isEmpty(x)) throw new Error('input list is empty');
+	assert(isNonEmpty(x));
+	_insertAfter(x, value);
+}

src/single.js

@@ -7,5 +7,5 @@ import Node from './Node.js';
  * @return {Node} The node at the front of the list.
  */
 export default function single(value) {
-	return new Node(value);
+	return new Node(value, null);
 }

src/unshift.js

@@ -1,10 +1,7 @@
 import assert from 'assert';
 
-// eslint-disable-next-line no-unused-vars
 import Node from './Node.js';
 import isList from './isList.js';
-import _setNext from './_setNext.js';
-import single from './single.js';
 
 /**
  * Unshift value to list.
@@ -15,7 +12,5 @@ import single from './single.js';
  */
 export default function unshift(x, value) {
 	assert(isList(x));
-	const y = single(value);
-	_setNext(y, x);
-	return y;
+	return new Node(value, x);
 }

test/src/api.js

@@ -15,6 +15,7 @@ import {
 	value,
 	setValue,
 	values,
+	insertAfter,
 } from '../../src/index.js';
 
 const toArray = (first) => list(values(first));
@@ -28,6 +29,7 @@ test('API', (t) => {
 	t.throws(() => shift(A), {message: /empty/});
 	t.throws(() => value(A), {message: /empty/});
 	t.throws(() => setValue(A, {}), {message: /empty/});
+	t.throws(() => insertAfter(A, {}), {message: /empty/});
 	t.throws(() => last(A), {message: /empty/});
 
 	t.false(isLast(A));
@@ -73,4 +75,9 @@ test('API', (t) => {
 
 	t.deepEqual(toArray(A), [8, 2, 1, 4, 3, 7]);
 	t.deepEqual(toArray(B), []);
+
+	insertAfter(A, 9);
+	t.deepEqual(toArray(A), [8, 9, 2, 1, 4, 3, 7]);
+	insertAfter(last(A), 5);
+	t.deepEqual(toArray(A), [8, 9, 2, 1, 4, 3, 7, 5]);
 });