JSFiddle - React, Tailwind, and code Playground

JavaScript

function weekTemps(){
  this.datastore = [];
  this.add = add;
  this.average = average;
}

function add(temp) {
  this.datastore.push(temp);
}

function average() {
 var total = 0;
    for(var i=0; i < this.datastore.length; ++i) {
      total += this.datastore[i];
    } 
   return total/this.datastore.length; 
}

var thisweek = new weekTemps();
thisweek.add(54);
thisweek.add(56);
thisweek.add(58);
thisweek.add(60);
console.log(thisweek.average());