linked-list

Small double linked list.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • List([items…])
  • Item()
• Types
• Compatibility
• Security
• Contribute
• License

What is this?

This package is a small double linked list. Items in linked lists know about their next sibling (the item after them). In double linked lists, items also know about their previous sibling (the item before them).

When should I use this?

You can use this project as a reference for how to implement a linked list but it’s also definitely possible to use it, directly or by subclassing its lists and items.

Install

This package is ESM only. In Node.js (version 12.20+, 14.14+, or 16.0+), install with npm:

npm install linked-list

In Deno with esm.sh:

import {List, Item} from 'https://esm.sh/linked-list@3'

In browsers with esm.sh:

<script type="module">
  import {List, Item} from 'https://esm.sh/linked-list@3?bundle'
</script>

Use

import {List, Item} from 'linked-list'

var item1 = new Item()
var item2 = new Item()
var item3 = new Item()
var list = new List(item1, item2, item3)

list.head // => item1
list.head.next // => item2
list.head.next.next // => item3
list.head.next.prev // => item1
list.tail // => item3
list.tail.next // => `null`

Subclassing:

import {List, Item} from 'linked-list'

class Tokens extends List {
  join(delimiter) {
    return this.toArray().join(delimiter)
  }
}

class Token extends Item {
  constructor(value) {
    super()
    this.value = value
  }

  toString() {
    return this.value
  }
}

var dogs = new Token('dogs')
var and = new Token('&')
var cats = new Token('cats')
var tokens = new Tokens(dogs, and, cats)

console.log(tokens.join(' ')) // => 'dogs & cats'

and.prepend(cats)
and.append(dogs)

console.log(tokens.join(' ') + '!') // => 'cats & dogs!'

API

This package exports the following identifiers: List, Item. There is no default export.

List([items…])

new List()
new List(new Item(), new Item())

Create a new linked list.

List.from([items])

List.from()
List.from([])
List.from([new Item(), new Item()])

Create a new this and adds the given array of items. Ignores null or undefined values. Throws an error when a given item has no detach, append, or prepend methods.

List.of([items…])

List.of()
List.of(new Item(), new Item())

Creates a new linked list from the given arguments. Defers to List.from.

List#append(item)

var list = new List()
var item = new Item()

list.head === null // => true
item.list === null // => true

list.append(item)

list.head === item // => true
item.list === list // => true

Appends an item to a list. Throws an error when the given item has no detach, append, or prepend methods. Returns the given item.

List#prepend(item)

var list = new List()
var item = new Item()

list.prepend(item)

Prepends an item to a list. Throws an error when the given item has no detach, append, or prepend methods. Returns the given item.

List#toArray()

var item1 = new Item()
var item2 = new Item()
var list = new List(item1, item2)
var array = list.toArray()

array[0] === item1 // => true
array[1] === item2 // => true
array[0].next === item2 // => true
array[1].prev === item1 // => true

Returns the items in the list in an array.

List#head

var item = new Item()
var list = new List(item)

list.head === item // => true

The first item in a list, and null otherwise.

List#tail

var list = new List()
var item1 = new Item()
var item2 = new Item()

list.tail === null // => true

list.append(item1)
list.tail === null // => true, see note.

list.append(item2)
list.tail === item2 // => true

The last item in a list, and null otherwise. Note that a list with only one item has no tail, only a head.

List#size

var list = new List()
var item1 = new Item()
var item2 = new Item()

list.size === 0 // => true

list.append(item1)
list.size === 1 // => true

list.append(item2)
list.size === 2 // => true

The number of items in the list.

Item()

var item = new Item()

Creates a new linked list Item.

Item#append(item)

var item1 = new Item()
var item2 = new Item()

new List().append(item1)

item1.next === null // => true

item1.append(item2)
item1.next === item2 // => true

Adds the given item after the operated on item in a list. Throws an error when the given item has no detach, append, or prepend methods. Returns false when the operated on item is not attached to a list, otherwise the given item.

Item#prepend(item)

var item1 = new Item()
var item2 = new Item()

new List().append(item1)

item1.prev === null // => true

item1.prepend(item2)
item1.prev === item2 // => true

Adds the given item before the operated on item in a list. Throws an error when the given item has no detach, append, or prepend methods. Returns false when the operated on item is not attached to a list, otherwise the given item.

Item#detach()

var item = new Item()
var list = new List(item)

item.list === list // => true

item.detach()
item.list === null // => true

Removes the operated on item from its parent list. Removes references to it on its parent list, and prev and next items; relinking them when possible. Returns the operated on item. Even when it was already detached.

Item#next

var item1 = new Item()
var item2 = new Item()

new List(item1)

item1.next === null // => true
item2.next === null // => true

item1.append(item2)

item1.next === item2 // => true

item1.detach()

item1.next === null // => true

The items succeeding item, and null otherwise.

Item#prev

var item1 = new Item()
var item2 = new Item()

new List(item1)

item1.prev === null // => true
item2.prev === null // => true

item1.append(item2)

item1.prev === item2 // => true

item2.detach()

item2.prev === null // => true

The items preceding item, and null otherwise.

Item#list

var item = new Item()
var list = new List()

item.list === null // => true

list.append(item)

item.list === list // => true

item.detach()

item.list === null // => true

The items parent list, and null otherwise.

Types

This package is fully typed with TypeScript. There are no extra exported types.

Compatibility

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. It also works in Deno and modern browsers.

Security

This package is safe.

Contribute

Yes please! See How to Contribute to Open Source.

License

MIT © Titus Wormer