Access nested array of objects

Question

im having real trouble to complete an FullStackOpen exersice, it requires to render some data to the page. Give the next code, i have to render the number of Parts that each Course has, and also so reduce the number of Parts/Exersices to render the total of exersices por each Course.

I am not being able to reach the inside of the Parts array of objects

    {
      name: "Half Stack application development",
      id: 1,
      parts: [
        {
          name: "Fundamentals of React",
          exercises: 10,
          id: 1,
        },
        {
          name: "Using props to pass data",
          exercises: 7,
          id: 2,
        },
        {
          name: "State of a component",
          exercises: 14,
          id: 3,
        },
        {
          name: "Redux",
          exercises: 11,
          id: 4,
        },
      ],
    },
    {
      name: "Node.js",
      id: 2,
      parts: [
        {
          name: "Routing",
          exercises: 3,
          id: 1,
        },
        {
          name: "Middlewares",
          exercises: 7,
          id: 2,
        },
      ],
    },
  ];``` 

Answer 1

It's not that difficult, for each element of the array:

• number of parts is currentElement.parts.length
• number of exercises can be computed using Array.reduce

const data = [
  {
    name: "Half Stack application development",
    id: 1,
    parts: [{
        name: "Fundamentals of React",
        exercises: 10,
        id: 1,
      },
      {
        name: "Using props to pass data",
        exercises: 7,
        id: 2,
      },
      {
        name: "State of a component",
        exercises: 14,
        id: 3,
      },
      {
        name: "Redux",
        exercises: 11,
        id: 4,
      },
    ],
  },
  {
    name: "Node.js",
    id: 2,
    parts: [{
        name: "Routing",
        exercises: 3,
        id: 1,
      },
      {
        name: "Middlewares",
        exercises: 7,
        id: 2,
      },
    ],
  },
];

const res = []

for (const course of data) {
  const tmpObj = {
    courseName: course.name,
    parts: course.parts.length,
    exercises: course.parts.reduce((a,b) => a + b.exercises, 0)
  }
  
  res.push(tmpObj)
}

console.log(res)