ES6 implementation of the FIFO queue data structure with TypeScript support.
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yarn add kiu
npm install kiu
A queue is a linear data structure, or more abstractly a sequential collection, in which the entities are kept in order and the principal operations are the addition of entities to the rear terminal position, known as enqueue, and removal of entities from the front terminal position, known as dequeue. This makes the queue a FIFO, First-In-First-Out, data structure. In this FIFO data structure, the first element added to the queue will be the first one to be removed. Once a new element is added, all elements that were added previously have to be removed before the new one can. Additionally, a peekFirst operation returns the value of the front element without dequeuing it, and a peakLast operation returns the value of the rear element, without mutating the queue as well. Kiu FIFO queues use a linear doubly linked list as their backbone, giving an efficient O(1) performance for the enqueuing and dequeuing operations.
Kiu exposes a chainable API, that can be utilized through a simple and minimal syntax, allowing you to combine methods effectively.
Usage examples can be also found at the test directory.
'use strict';
const {Queue} = require('kiu');
const queue = new Queue();
//=> Queue { head: null, last: null, length: 0 }
queue.isEmpty();
//=> true
queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, next: null, prev: null },
// last: Item { value: 10, next: null, prev: null },
// length: 1 }
queue.isEmpty();
//=> false
queue.peekFirst();
//=> 10
queue
.enqueue(20)
.enqueue(30)
.enqueue(40)
.enqueue(50);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 50, next: null, prev:
// Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.includes(30);
//=> true
queue.includes(60);
//=> false
queue.dequeue();
//=> 10
queue.peekFirst();
//=> 20
queue.peekLast();
//=> 50
queue.toArray();
//=> [ 20, 30, 40, 50 ]
queue.rotateRight(1);
//=> Queue {
// head:
// Item { value: 30, prev: null, next:
// Item { value: 40, prev: [Circular], next: [Item] } },
// last:
// Item { value: 20, next: null, prev:
// Item { value: 50, next: [Circular], prev: [Item] } },
// length: 4 }
queue.toArray();
//=> [ 30, 40, 50, 20 ]
queue.rotateLeft(3);
//=> Queue {
// head:
// Item { value: 40, prev: null, next:
// Item { value: 50, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 4 }
queue.toArray();
//=> [ 40, 50, 20, 30 ]
queue
.reverse()
.map(x => x * 10)
.toArray();
//=> [ 300, 200, 500, 400 ]
queue.nth(2);
//=> 500
lengthNumberReturns the total number of values in the queue.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: null } },
// last:
// Item { value: 20, next: null, prev:
// Item { value: 10, next: [Circular], prev: null } },
// length: 2 }
queue.length;
//=> 2
clear()QueueMutates the queue by removing all residing values and returns it empty.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.length;
//=> 3
queue.clear();
//=> Queue { head: null, last: null, length: 0 }
queue.length;
//=> 0
dequeue()Any | undefinedMutates the queue by removing the value located at the front terminal position. Returns the removed value, if the queue is not empty, or undefined if it is.
const {Queue} = require('kiu');
const queue = new Queue();
queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.dequeue();
//=> 10
queue.dequeue();
//=> undefined
enqueue(value)QueueMutates the queue by inserting a new value at the rear terminal position. Returns the queue itself.
valueAnyValue to insert.
const {Queue} = require('kiu');
const queue = new Queue();
queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.enqueue(20).enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.length;
//=> 3
forEach(fn)QueueTraverses the queue, from the front to the rear, and executes the provided fn function once for each traversed value, without mutating the queue. Returns the queue itself at the end of the traversal.
fnFunctionUnary function to execute for each traversed value.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.forEach(console.log);
//=> 10
// 20
// 20
includes(value)BooleanDetermines whether the queue includes a certain value, returning true or false as appropriate.
valueAnyValue to search for.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.includes(10);
//=> true
queue.includes(40);
//=> false
queue.includes(20);
//=> true
isEmpty()BooleanDetermines whether the queue is empty, returning true or false as appropriate.
const {Queue} = require('kiu');
const queue = new Queue();
queue.isEmpty();
//=> true
queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.isEmpty();
//=> false
map(fn)QueueTraverses the queue, from front to rear, and mutates it by updating each stored value with the result of calling once the provided fn function on it. Returns the in-place mutated queue at the end of the traversal.
fnFunctionUnary function that produces a value of the mutated queue.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.map(x => x * 10);
//=> Queue {
// head:
// Item { value: 100, prev: null, next:
// Item { value: 200, prev: [Circular], next: [Item] } },
// last:
// Item { value: 300, next: null, prev:
// Item { value: 200, next: [Circular], prev: [Item] } },
// length: 3 }
nth(n)Any | undefinedTraverses the queue, from front to rear, and returns the nth value. If the value does not exist, then undefined is returned. The queue values follow zero-based numbering, thus the first/initial value corresponds to index 0.
nNumberZero-based queue index number.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.nth(0);
//=> 10
queue.nth(2);
//=> 30
queue.nth(3);
//=> undefined
peekFirst()Any | undefinedReturns the first value, located at the front of the queue, without mutating the queue itself. If the queue is empty, then undefined is returned.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.peekFirst();
//=> 10
peekLast()Any | undefinedReturns the last value, located at the rear of the queue, without mutating the queue itself. If the queue is empty, then undefined is returned.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.peekLast();
//=> 30
reverse()QueueMutates the queue by reversing in-place the residing values. The first value becomes the last one, and the last one becomes the first. Returns the reversed queue.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.toArray();
//=> [ 10, 20, 30 ]
queue.reverse();
//=> Queue {
// head:
// Item { value: 30, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 10, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.toArray();
//=> [ 30, 20, 10 ]
rotateLeft(n)QueueMutates the queue by moving the n rear-most values to the front of the queue in a rotating fashion. Returns the queue itself.
nNumberNumber of rear-most values to be rotated.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30)
.enqueue(40)
.enqueue(50);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 50, next: null, prev:
// Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]
queue.rotateLeft(2);
//=> Queue {
// head:
// Item { value: 40, prev: null, next:
// Item { value: 50, prev: [Circular], next: [Item] } },
// last:
// Item { value: 30, next: null, prev:
// Item { value: 20, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 40, 50, 10, 20, 30 ]
rotateRight(n)QueueMutates the queue by moving the n front-most items to the rear of the queue in a rotating fashion. Returns the queue itself.
nNumberNumber of front-most values to be rotated.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30)
.enqueue(40)
.enqueue(50);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 50, next: null, prev:
// Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]
queue.rotateRight(2);
//=> Queue {
// head:
// Item { value: 30, prev: null, next:
// Item { value: 40, prev: [Circular], next: [Item] } },
// last:
// Item { value: 20, next: null, prev:
// Item { value: 10, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 30, 40, 50, 10, 20 ]
toArray()Array<Any>The method traverses the queue, from front to rear, and stores each traversed value in an array. The array is returned at the end of the traversal.
const {Queue} = require('kiu');
const queue = new Queue();
queue
.enqueue(10)
.enqueue(20)
.enqueue(30)
.enqueue(40)
.enqueue(50);
//=> Queue {
// head:
// Item { value: 10, prev: null, next:
// Item { value: 20, prev: [Circular], next: [Item] } },
// last:
// Item { value: 50, next: null, prev:
// Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]
For more info on how to contribute to the project, please read the contributing guidelines.
cd kiunpm install or yarn installnpm test or yarn testFAQs
FIFO Queues for ES6
The npm package kiu receives a total of 1 weekly downloads. As such, kiu popularity was classified as not popular.
We found that kiu demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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