normalize-solution.js

// https://gist.github.com/nishanbajracharya/8fe38807b3ad074a7da2072c7b8e701b

function normalize(input = {}) {
  var values = Array.isArray(input) ? input : Object.values(input);

  return values.reduce((acc, value) => {
    if (value.children) {
      return {
        ...acc,
        [value.id]: {
          id: value.id,
          name: value.name,
          children: value.children.map((child) => child.id),
        },
        ...normalize(value.children),
      };
    }

    return {...acc, [value.id]: value};
  }, {});
}

var result = normalize(input);