Reduce an array of objects

Question

The object looks like this: My App.js file looks like this

const course = {
    id: 1,
    name: "Half Stack application development",
    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,
      },
    ],
  };
return <Course course={course} />;

And I want to total number of exercises filtered into total

const parts = props.Course.parts;

const total = parts.reduce((previousValue, currentValue) => {
    return previousValue + currentValue;
  }, 0);

Output is shown as:

0[object Object][object Object][object Object][object Object]

return previousValue + currentValue.excercises should probably do. — Wiktor Zychla
– Wiktor Zychla, Commented Sep 5, 2022 at 8:31
Remember Course (capital "C") is not the same as course (small "c") for JavaScript. const parts = props.Course.parts; should be const parts = props.course.parts;. Furthermore, as @WiktorZychla already pointed out, you have to access the exercises attribute of the current items. — secan
– secan, Commented Sep 5, 2022 at 8:35

Utkarsh Dixit · Accepted Answer · 2022-09-05 08:36:54Z

1

As pointed out by @wiktor-zychla, adding exercises in your reduce function will work.

const parts = props.course.parts;

const total = parts.reduce((previousValue, currentValue) => {
    return previousValue + currentValue.excercises;
  }, 0);

Explanation behind your original output,

0[object Object][object Object][object Object][object Object]

The above output is the result of adding object to a number. Hope this helps

Edit: There was also typo in how you are accessing course prop. Fixed it above

answered Sep 5, 2022 at 8:36

Utkarsh Dixit

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