Data Structures: Create a Priority Queue Class

JavaScript
1

My code for priority queue is failing one test: “The priority queue should return items with a higher priority before items with a lower priority and return items in first-in-first-out order otherwise.”

    this.enqueue = function(element){
      if(this.isEmpty())
        this.collection.push(element);
      else if(this.collection[this.size() - 1][1] > element[1]) 
        this.collection.push(element);
      else if(this.collection[0][1] <= element[1]) 
        this.collection.unshift(element)
      else{
        for(let i = 1; i < this.size(); i++){
          if(element[1] >= this.collection[i][1]){
            this.collection.splice(i, 0, element);
            break;
          }
        }
      }
      
    }

    this.dequeue = function(){
      return this.collection.pop();
    }

    this.front = function(){
      return this.collection[this.collection.length];
    }

    this.isEmpty = function(){
      return this.collection.length == 0;
    }

    this.size = function(){
      return this.collection.length;
    }