1. A queue is a group of ordered items following the first in first out (FIFO) principle. Elements are added at the end of the queue and removed from the top. The newly added elements must be at the end of the queue. Common examples in life, such as queuing.

2. Create a queue class

class Queue{
    constructor(){
        this.count = 0;//Number of queue records
        this.lowestCount = 0;//Records the position of the current queue head
        this.items = [];//Used to store elements.
    }
}

3. Add elements

  enqueue(element){
        this.items[this.count] = element;
        this.count++;
    }

4. Delete element (only delete queue header)

    dequeue(){
        if(this.isEmpty()){
            return 'queue is null';
        }
        let resulte = this.items[this.lowestCount];
        delete  this.items[this.lowestCount];
        this.lowestCount++;
        return resulte;
    }

5. View the queue header elements

    peek(){
        return this.items[this.lowestCount];
    }

6. Judge whether the queue is empty

    isEmpty(){
        return this.count - this.lowestCount === 0;
    }

7. Clear the elements of the queue

    clear(){
        this.count = 0;
        this.lowestCount = 0;
        this.items = [];
    }

8. Check the length of the queue

 size(){
        return this.count - this.lowestCount;
    }

9. View all contents of the queue

  toString(){
        if(this.isEmpty())return "queue is null";
        let objString = this.items[this.lowestCount];
        for(let i = this.lowestCount+1; i < this.count;i++){
            objString = `${objString},${this.items[i]}`;
        }
        return objString;
    }

10. Complete code

class Queue{
    constructor(){
        this.count = 0;//Number of queue records
        this.lowestCount = 0;//Records the position of the top of the current queue
        this.items = [];//Used to store elements.
    }
    enqueue(element){
        this.items[this.count] = element;
        this.count++;
    }
    dequeue(){
        if(this.isEmpty()){
            return 'queue is null';
        }
        let resulte = this.items[this.lowestCount];
        delete  this.items[this.lowestCount];
        this.lowestCount++;
        return resulte;
    }
    peek(){
        return this.items[this.lowestCount];
    }
    isEmpty(){
        return this.count - this.lowestCount === 0;
    }
    size(){
        return this.count - this.lowestCount;
    }
    clear(){
        this.count = 0;
        this.lowestCount = 0;
        this.items = [];
    }
    toString(){
        if(this.isEmpty())return "queue is null";
        let objString = this.items[this.lowestCount];
        for(let i = this.lowestCount+1; i < this.count;i++){
            objString = `${objString},${this.items[i]}`;
        }
        return objString;
    }
}

11. Operation results