Javascript Data Structure Tutorial - Javascript Queue

The two primary operations involving queues are inserting a new element into a queue and removing an element from a queue.

The insertion operation is called enqueue, and the removal operation is called dequeue.

The enqueue operation inserts a new element at the end of a queue, and the dequeue operation removes an element from the front of a queue.

Example


function Queue() { //from   w w w .ja  va2s  .c  o m
    this.dataStore = []; 
    this.enqueue = enqueue; 
    this.dequeue = dequeue; 
    this.front = front; 
    this.back = back; 
    this.toString = toString; 
    this.empty = empty; 
} 
//The enqueue() function adds an element to the end of a queue: 
function enqueue(element) { 
    this.dataStore.push(element); 
} 
//The dequeue() function removes an element from the front of a queue: 
function dequeue() { 
    return this.dataStore.shift(); 
} 
//examine the front and back elements of a queue using these functions: 
function front() { 
    return this.dataStore[0]; 
} 

function back() { 
    return this.dataStore[this.dataStore.length-1]; 
} 
//toString() function to display all the elements in a queue: 
function toString() { 
    var retStr = ""; 
    for (var i = 0; i < this.dataStore.length; ++i) { 
        retStr += this.dataStore[i] + "\n"; 
    } 
    return retStr; 
} 
//if a queue is empty: 
function empty() { 
    if (this.dataStore.length == 0) { 
        return true; 
    } else { 
        return false; 
    } 
} 

var q= new Queue(); 
q.enqueue("M"); 
q.enqueue("C"); 
q.enqueue("J"); 
console.log(q.toString()); 
q.dequeue(); 
console.log(q.toString()); 
console.log("Front of queue: " + q.front()); 
console.log("Back of queue: " + q.back());

The code above generates the following result.

Example 2

The following code shows how to create a Queue data structure.


var Queue = function() {
  this.storage = {};// ww w.jav a 2 s  .c o m
  this.front = 0;
  this.queueSize = 0;
};

Queue.prototype.enqueue = function(value) {
  this.storage[this.queueSize++] = value;
};
Queue.prototype.dequeue = function() {
  if (this.queueSize - this.front) {
    var temp = this.storage[this.front];
    return (delete this.storage[this.front++]) && temp;
  }
};
Queue.prototype.size = function(value) {
  return this.queueSize - this.front;
};