Immutable object update

immutable_update.js

// Based on 'Easy immutable objects in Javascript'
// https://spapas.github.io/2018/04/05/easy-immutable-objects/

const immutable_update = (obj, path, val) => {
  if (!val) {
    return path.reduce((obj, [path, val]) => immutable_update(obj, path, val), obj);
  }

  let parts = (typeof path === 'string' || path instanceof String) ? path.split('.') : path;

  const cset = (obj, cidx, val) => {
    let newval = val;
    if (typeof val === "function") {
      newval = val(obj[cidx]);
    }

    if (Array.isArray(obj)) {
      return [...obj.slice(0, cidx * 1), newval, ...obj.slice(cidx * 1 + 1)];
    } else {
      return { ...obj, [cidx]: newval };
    }
  };

  let pidx = parts[0];

  if(parts.length == 1) {
    return cset(obj, pidx, val);
  } else {
    let remaining = parts.slice(1);
    return cset(obj, pidx, immutable_update(obj[pidx], remaining, val));
  }
};

const state = {
  'users': {
    'results': [
      {'name': 'Sera', 'groups': ['g1', 'g2', 'g3']},
      {'name': 'John', 'groups': ['g1', 'g2', 'g3']},
      {'name': 'Joe', 'groups': []}
    ],
    'pagination': {
      'total': 100,
      'perpage': 5,
      'number': 0
    }
  },
  'groups': {
    'results': [],
    'total': 0
  }
};


const path_and_value_list = [
  ['users.results.2.groups.0', 'aa'],
  ['users.results.0.name', (x) => x.toUpperCase()],
  ['users.pagination.total', (x) => x + 1],
  ['users.results.1.name', 'Jack']
];

console.log(state);
console.log(immutable_update(state, path_and_value_list));