How to call JavaScript reduce() on an object?

To call JavaScript reduce() on an object, we can use the Object.values method.

For instance, we write

const o = {
  a: { value: 1 },
  b: { value: 2 },
  c: { value: 3 },
};

Object.values(o).reduce((previous, entry) => {
  return previous + entry.value;
}, 0);

to call Object.values with o to return an array of object property values in o.

Then we call reduce with a callback that returns the sum of the previous partial sum plus the entry.value value.

entry is the o property value being looped through.