class Quene {
	  constructor() {
	    this.data = [];
	    this.front = 0;
	    this.rear = 0;
		}
		push(elm) {
			this.data[this.rear] = elm;
      this.rear++;
		}
		pop() {
	    if(this.isEmpty()) {
	      return console.error('队列已经为空了，这次操作为下溢');
			}
			return this.data[this.front++];
		}
		size() {
			return this.rear - this.front;
		}
		isEmpty() {
			return this.front === this.rear;
		}
		clear() {
			this.front = this.rear = 0;
		}
	}

	var q = new Quene();
  q.push(1);
  q.push(2);
  q.size(); // 2
  q.pop();
  q.pop();
  q.isEmpty(); // true
  q.pop();// error
  q.push(1);
  q.push(2);
  q.clear();
  console.log(q.isEmpty()); // true