Generic Skill Challenge

solution.ts

//an alternate (and perhaps better approach)
interface IWeightedItem{
  weight: number
}

interface Grade extends IWeightedItem{
  score: number;
}

interface Product extends IWeightedItem{
  price: number;
}

enum HitType {
  noHitter,
  single,
  double,
  triple,
  homerun
}

interface BaseballHitRecord extends IWeightedItem{
  hit: HitType
}

const weightedAverage = <T extends IWeightedItem>(arr: T[], valueSelector: (item: T) => number) => {
  let totalWeight = 0;
  let totalValue = 0;
  for (let item of arr) {
    totalWeight += item.weight;
    totalValue += item.weight * valueSelector(item); 
  }
  return totalValue / totalWeight;
}


let grades: Grade[] = [
  {
    weight: 3,
    score: 100
  },
  {
    weight: 1,
    score: 60
  },
  {
    weight: 1,
    score: 20
  },
  {
    weight: 1,
    score: 40
  },
];

const test = (value: number, expected: number) => {
  if (value === expected) {
    alert('pass!')
  } else {
    alert('fail!')
  }
}

let weightedGrades = weightedAverage(grades, (grade) => grade.score);
test(weightedGrades, 70);