setting state helper.js

const REMOVE = () => REMOVE;
const get = (object, path, defaultValue) => {
  const recur = (current, path, defaultValue) => {
    if (current === undefined) {
      return defaultValue;
    }
    if (path.length === 0) {
      return current;
    }
    return recur(
      current[path[0]],
      path.slice(1),
      defaultValue
    );
  };
  return recur(object, path, defaultValue);
};
const set = (object, path, callback) => {
  const setKey = (current, key, value) => {
    if (Array.isArray(current)) {
      return value === REMOVE
        ? current.filter((_, i) => key !== i)
        : current.map((c, i) => (i === key ? value : c));
    }
    return value === REMOVE
      ? Object.entries(current).reduce((result, [k, v]) => {
          if (k !== key) {
            result[k] = v;
          }
          return result;
        }, {})
      : { ...current, [key]: value };
  };
  const recur = (current, path, newValue) => {
    if (path.length === 1) {
      return setKey(current, path[0], newValue);
    }
    return setKey(
      current,
      path[0],
      recur(current[path[0]], path.slice(1), newValue)
    );
  };
  const oldValue = get(object, path);
  const newValue = callback(oldValue);
  if (oldValue === newValue) {
    return object;
  }
  return recur(object, path, newValue);
};
const data = {
  name: [{ hello: 'world', stay: true }, 4],
  list: [1, 2, 3],
};
console.log(
  'setting nested value',
  set(data, ['name', 0, 'hello'], () => 'hello world')
    .name[0].hello
);
console.log(
  'doubling nested value',
  set(data, ['name', 1], x => x * 2).name[1]
);
console.log(
  'removing nested value',
  set(data, ['name', 0, 'hello'], REMOVE).name[0]
);
console.log(
  'adding to an array',
  set(data, ['list'], v => [...v, 4]).list
);
console.log(
  'mapping an array',
  set(data, ['list'], v => v.map(v => v * 8)).list
);
console.log(
  'return same reference if nothing changed',
  set(data, ['list'], x => x) === data
);
console.log(
  'data is not mutated',
  JSON.stringify(data, undefined, 2)
);