discord.js/src/structures/shared/resolvePermissions.js

const Permissions = require('../../util/Permissions');
const Collection = require('../../util/Collection');

module.exports = function resolvePermissions(overwrites) {
  if (overwrites instanceof Collection || overwrites instanceof Array) {
    overwrites = overwrites.map(overwrite => {
      const role = this.guild.roles.resolve(overwrite.id);
      if (role) {
        overwrite.id = role.id;
        overwrite.type = 'role';
      } else {
        overwrite.id = this.client.users.resolveID(overwrite.id);
        overwrite.type = 'member';
      }

      return {
        allow: Permissions.resolve(overwrite.allowed || 0),
        deny: Permissions.resolve(overwrite.denied || 0),
        type: overwrite.type,
        id: overwrite.id,
      };
    });
  }

  return overwrites;
};