How to calculate the average rating like in mongoDB, only in pure js?

Question

JavaScript

I have a post:

post: {
      title: "Future devops", 
      avgrating: 5, 
      ratingOne: 4
      ratingTwo: 4 
      ratingThree: 4       
      ratingFour: 5 
      ratingFive: 4
    }

and comments on it

commentsPost: [
      {
      name: "Dima", 
      ratingOne: 3,
      ratingTwo: 2,
      ratingThree: 2,      
      ratingFour: 5,
      ratingFive: 2
      },
      {
      name: "Dima", 
      ratingOne: 3,
      ratingTwo: 2,
      ratingThree: 2,      
      ratingFour: 5,
      ratingFive: 2
      },
      {
      name: "Dima", 
      ratingOne: 3,
      ratingTwo: 2,
      ratingThree: 2,      
      ratingFour: 5,
      ratingFive: 2
      },
      {
      name: "Dima", 
      ratingOne: 3,
      ratingTwo: 2,
      ratingThree: 2,      
      ratingFour: 5,
      ratingFive: 2
      },
      {
      name: "Dima", 
      ratingOne: 3,
      ratingTwo: 2,
      ratingThree: 2,      
      ratingFour: 5,
      ratingFive: 2
      },
     ]

The maximum score of the parameter is 5 points.

I want to calculate the average rating for each Post's rating field based on the total number of comments and their ratings.

That is, each Post field (ratingOne, ratingTwo, ratingThree,
ratingFour, ratingFive) has an average value for the number of comments. And the post's avgrating field has an average score based on the rest of the Post's rating fields (ratingOne, etc.).

The bottom line is that people put ratings on 5 parameters (speed, accessibility, etc.) and based on this, the overall rating of the service and the overall rating for each parameter are calculated. In order to evaluate the service in detail for each parameter.

I'm scratching my head, but I can't think of a better way to implement it. Mongoose has a parameter for this and everything is done there in a couple of lines, but I need to implement this in pure js, since I use graphcms, and there is no such possibility as aggregate - avg, only count.