onFieldChange implementation with validation

onFieldChange.js

import {action, observable} from 'mobx';
import Validator from 'validatorjs';

class LoginStore {
  @observable
  form = {
    fields: {
      email: {
        value: '',
        error: null,
        rule: 'required|email'
      },
      password: {
        value: '',
        error: null,
        rule: 'required'
      },
    },
    meta: {
      isValid: true,
      error: null,
    },
  }
  @action
  onFieldChange = (field, value) => {
    this.form.fields[field].value = value;
    let {email, password} = this.form.fields
    var validation = new Validator(
      {email: email.value, password: password.value},
      {email: email.rule, password: password.rule},
    )
    this.form.meta.isValid = validation.passes();
    this.form.fields[field].error = validation.errors.first(field)
  };
}
export default LoginStore;