linkedList.js

// To run: copy this file (or open it using the "Raw" button in the right-hand corner) and save it as linkedList.js
// Then in the terminal, run `node linkedList.js | less` to view output and compare expected to actual values.

class LinkedList {

  constructor(firstItem) {
    this.list = {
      data: firstItem,
      link: {}
    };
  }

  insertBefore(nodeToInsertBefore, newNode) {
    var node = this.findPrevNode(nodeToInsertBefore);
    var oldNode = Object.assign({}, node.link);
    node.link = {data: newNode, link: oldNode};
  }

  insertAfter(nodeToInsertAfter, newNode) {
    var node = this.findNode(nodeToInsertAfter, this.list);
    var oldNode = Object.assign({}, node.link);
    node.link = {data: newNode, link: oldNode};
  }

  findNode(dataAtNode, nodeToStartAt=this.list) {
    if (nodeToStartAt.data === dataAtNode) {
      return nodeToStartAt;
    }
    return this.findNode(dataAtNode, nodeToStartAt.link);
  }

  findPrevNode(dataAtNode, prevNode=null, nodeToStartAt=this.list) {
    if (nodeToStartAt.data === dataAtNode) {
      return prevNode;
    }
    return this.findPrevNode(dataAtNode, nodeToStartAt, nodeToStartAt.link);
  }

}

function test() {

  var list = new LinkedList('words');
  // {data: words, link: {}}

  list.insertAfter('words', 'more words');
  // {data: words, link: {data: more words, link: {}}}

  list.insertAfter('more words', 'yet more');
  // {data: words, link: {data: more words, link: {data: yet more, link: {}}}}

  list.insertAfter('words', 'moar');
  // {data: words, link: {data: moar, link: {data: more words, link: {data: yet more, link: {}}}}

  var foundNode = list.findNode('moar');
  // {data: moar, link: {data: more words, link: {data: yet more, link {}}}}
  var shouldHaveFoundNode = {data: 'moar', link: {data: 'more words', link: {data: 'yet more', link: {}}}};
  console.log('searched for node where "data" is "moar"; should have found:\n', JSON.stringify(shouldHaveFoundNode, null, 2));
  console.log('actually found:\n', JSON.stringify(foundNode, null, 2));

  list.insertBefore('more words', 'WURD');
  // {data: words, link: {data: moar, link: {data: WURD, link: {data: more words, link: {data: yet more, link: {}}}}

  var finalList = {data: 'words', link: {data: 'moar', link: {data: 'WURD', link: {data: 'more words', link: {data: 'yet more', link: {}}}}}};
  console.log('final list should look like: \n', JSON.stringify(finalList, null, 2));
  console.log('actual list is:\n');
  console.log(JSON.stringify(list.list, null, 2));
}

test();