data-structure-algebra/doubly-linked-list

import assert from 'assert';

import Node from './Node.js';

/**
 * Push value to list.
 *
 * @param {Node} z Last node of first input list (can be null).
 * @param {any} value Value to push.
 * @return {Node} The node at the front of the list (new node if empty, input
 * node otherwise).
 */
export default function _push(z, value) {
    assert(z instanceof Node);
    assert(z.next === null);
    const y = new Node(value, z, null);
    z.next = y;
    return y;
}