index.js

const _ = require("lodash");
const { defineAbility, an } = require("@casl/ability");
const { permittedFieldsOf } = require("@casl/ability/extra");

function Article(attrs) {
  Object.assign(this, attrs);
}

const user = {
  id: 1,
  age: 2,
  roles: [
    {
      id: 1,
      name: "admin",
      permissions: [
        {
          action: "read",
          subject: "Article",
          fields: ["author.name", "author.compo", "author.compo.compo.field"],
          conditions: ["isOwner", "userIs21"],
        },
      ],
    },
  ],
};

const conditionGenerators = {
  userIs21: (user) => {
    if (user.age === 21) {
      return true;
    }

    return false;
  },
  isOwner: (user) => ({ "created_by.id": user.id }),
};

const ability = defineAbility((allow) => {
  user.roles.forEach((role) => {
    role.permissions.forEach((perm) => {
      if (perm.conditions && perm.conditions.length > 0) {
        perm.conditions.forEach((cond) => {
          const condition = conditionGenerators[cond](user);

          if (condition === false) return; // if the generators returns false it means the permission should not be given.
          if (condition === true) {
            return allow(perm.action, perm.subject, perm.fields);
          }

          return allow(perm.action, perm.subject, perm.fields, condition);
        });
      } else {
        return allow(perm.action, perm.subject, perm.fields);
      }
    });
  });
});

const article = new Article({
  author: {
    name: "Georges",
  },
  created_by: {
    id: 1,
  },
});

console.log(ability.can("read", article, "author.name"));

// const data = ability.rulesFor("read", article).filter(article);

const allowedFields = permittedFieldsOf(ability, "read", article);
console.log(allowedFields);

console.log(_.pick(article, allowedFields));