the complexity comes from relying on a complex accumulator object instead just returning the average number ;)

avg_with_reduce.js

const basket = [
  { name:"apple", type: "fruit", calories: 52 }, 
  { name:"broccoli", type: "vegetable", calories: 45 },
  { name:"banana", type: "fruit", calories: 89 }
];

class CaloriesAccumulator {
  constructor(fruitCount = 0, avgCalories = 0) {
    console.debug(`count: ${fruitCount}\tavg: ${avgCalories}`)
    this.fruitCount = fruitCount
    this.avgCalories = avgCalories
  }  
}

const { avgCalories } = basket.reduce((acc, currentFood) => {
  if (currentFood.type !== "fruit"){
    return acc;
  }
   
  const newFruitCount = acc.fruitCount + 1;
  const previousTotalCalories = acc.avgCalories * acc.fruitCount;
  const newAvgCalories = (previousTotalCalories + currentFood.calories) / newFruitCount;
  
  return new CaloriesAccumulator(newFruitCount, newAvgCalories);
}, new CaloriesAccumulator());