Denque

Extremely fast and lightweight double-ended queue implementation with zero dependencies.

Double-ended queues can also be used as a:

• Stack
• Queue

This implementation is currently the fastest available, even faster than double-ended-queue, see the benchmarks

Every queue operation is done at a constant O(1) - including random access from .peekAt(index).

Works on all node versions >= v0.10

Quick Start

npm install denque

const Denque = require("denque");

const denque = new Denque([1,2,3,4]);
denque.shift(); // 1
denque.pop(); // 4

API

• new Denque()
• new Denque(Array items)
• push(item)
• unshift(item)
• pop()
• shift()
• toArray()
• peekBack()
• peekFront()
• peekAt(int index)
• remove(int index, int count)
• removeOne(int index)
• splice(int index, int count, item1, item2, ...)
• isEmpty()
• clear()

new Denque() -> Denque

Creates an empty double-ended queue with initial capacity of 4.

var denque = new Denque();
denque.push(1);
denque.push(2);
denque.push(3);
denque.shift(); //1
denque.pop(); //3

---

new Denque(Array items) -> Denque

Creates a double-ended queue from items.

var denque = new Denque([1,2,3,4]);
denque.shift(); // 1
denque.pop(); // 4

---

push(item) -> int

Push an item to the back of this queue. Returns the amount of items currently in the queue after the operation.

var denque = new Denque();
denque.push(1);
denque.pop(); // 1
denque.push(2);
denque.push(3);
denque.shift(); // 2
denque.shift(); // 3

---

unshift(item) -> int

Unshift an item to the front of this queue. Returns the amount of items currently in the queue after the operation.

var denque = new Denque([2,3]);
denque.unshift(1);
denque.toString(); // "1,2,3"
denque.unshift(-2);
denque.toString(); // "-2,-1,0,1,2,3"

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pop() -> dynamic

Pop off the item at the back of this queue.

Note: The item will be removed from the queue. If you simply want to see what's at the back of the queue use peekBack() or .peekAt(-1).

If the queue is empty, undefined is returned. If you need to differentiate between undefined values in the queue and pop() return value - check the queue .length before popping.

var denque = new Denque([1,2,3]);
denque.pop(); // 3
denque.pop(); // 2
denque.pop(); // 1
denque.pop(); // undefined

Aliases: removeBack

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shift() -> dynamic

Shifts off the item at the front of this queue.

Note: The item will be removed from the queue. If you simply want to see what's at the front of the queue use peekFront() or .peekAt(0).

If the queue is empty, undefined is returned. If you need to differentiate between undefined values in the queue and shift() return value - check the queue .length before shifting.

var denque = new Denque([1,2,3]);
denque.shift(); // 1
denque.shift(); // 2
denque.shift(); // 3
denque.shift(); // undefined

---

toArray() -> Array

Returns the items in the queue as an array. Starting from the item in the front of the queue and ending to the item at the back of the queue.

var denque = new Denque([1,2,3]);
denque.push(4);
denque.unshift(0);
denque.toArray(); // [0,1,2,3,4]

---

peekBack() -> dynamic

Returns the item that is at the back of this queue without removing it.

If the queue is empty, undefined is returned.

var denque = new Denque([1,2,3]);
denque.push(4);
denque.peekBack(); // 4

---

peekFront() -> dynamic

Returns the item that is at the front of this queue without removing it.

If the queue is empty, undefined is returned.

var denque = new Denque([1,2,3]);
denque.push(4);
denque.peekFront(); // 1

---

peekAt(int index) -> dynamic

Returns the item that is at the given index of this queue without removing it.

The index is zero-based, so .peekAt(0) will return the item that is at the front, .peekAt(1) will return the item that comes after and so on.

The index can be negative to read items at the back of the queue. .peekAt(-1) returns the item that is at the back of the queue, .peekAt(-2) will return the item that comes before and so on.

Returns undefined if index is not a valid index into the queue.

var denque = new Denque([1,2,3]);
denque.peekAt(0); //1
denque.peekAt(1); //2
denque.peekAt(2); //3

denque.peekAt(-1); // 3
denque.peekAt(-2); // 2
denque.peekAt(-3); // 1

Note: The implementation has O(1) random access using .peekAt().

Aliases: get

---

remove(int index, int count) -> array

Remove number of items from the specified index from the list.

Returns array of removed items.

Returns undefined if the list is empty.

var denque = new Denque([1,2,3,4,5,6,7]);
denque.remove(0,3); //[1,2,3]
denque.remove(1,2); //[5,6]
var denque1 = new Denque([1,2,3,4,5,6,7]);
denque1.remove(4, 100); //[5,6,7]

---

removeOne(int index) -> dynamic

Remove and return the item at the specified index from the list.

Returns undefined if the list is empty.

var denque = new Denque([1,2,3,4,5,6,7]);
denque.removeOne(4); // 5
denque.removeOne(3); // 4
denque1.removeOne(1); // 2

---

splice(int index, int count, item1, item2, ...) -> array

Native splice implementation.

Remove number of items from the specified index from the list and/or add new elements.

Returns array of removed items or empty array if count == 0.

Returns undefined if the list is empty.

var denque = new Denque([1,2,3,4,5,6,7]);
denque.splice(denque.length, 0, 8, 9, 10); // []
denque.toArray() // [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
denque.splice(3, 3, 44, 55, 66); // [4,5,6]
denque.splice(5,4, 666,667,668,669); // [ 66, 7, 8, 9 ]
denque.toArray() // [ 1, 2, 3, 44, 55, 666, 667, 668, 669, 10 ]

---

isEmpty() -> boolean

Return true if this queue is empty, false otherwise.

var denque = new Denque();
denque.isEmpty(); // true
denque.push(1);
denque.isEmpty(); // false

---

clear() -> void

Remove all items from this queue. Does not change the queue's capacity.

var denque = new Denque([1,2,3]);
denque.toString(); // "1,2,3"
denque.clear();
denque.toString(); // ""

---

Benchmarks

Platform info:

Darwin 17.0.0 x64
Node.JS 9.4.0
V8 6.2.414.46-node.17
Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz × 8

1000 items in queue

(3 x shift + 3 x push ops per 'op')

denque x 64,365,425 ops/sec ±0.69% (92 runs sampled)
double-ended-queue x 26,646,882 ops/sec ±0.47% (94 runs sampled)

2 million items in queue

(3 x shift + 3 x push ops per 'op')

denque x 61,994,249 ops/sec ±0.26% (95 runs sampled)
double-ended-queue x 26,363,500 ops/sec ±0.42% (91 runs sampled)

Splice

(1 x splice per 'op') - initial size of 100,000 items

denque.splice x 925,749 ops/sec ±22.29% (77 runs sampled)
native array splice x 7,777 ops/sec ±8.35% (50 runs sampled)

Remove

(1 x remove + 10 x push per 'op') - initial size of 100,000 items

denque.remove x 2,635,275 ops/sec ±0.37% (95 runs sampled)
native array splice - Fails to complete: "JavaScript heap out of memory"

Remove One

(1 x removeOne + 10 x push per 'op') - initial size of 100,000 items

denque.removeOne x 1,088,240 ops/sec ±0.21% (93 runs sampled)
native array splice x 5,300 ops/sec ±0.41% (96 runs sampled)

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