React and MobX form validation - full example here https://github.com/mkozhukharenko/mobx-form-validation

get-values.js

// trun {fiels: {email: 'val', err:''}} to {email: 'val'}
var getValues = () => {
    let data = {};
    let form = toJS(this.form).fields;
    Object.keys(form).map(key => {
      data[key] = form[key].value
    });
    return data
}

login-form.store.js

import {action} from 'mobx'
var Validator = require('validatorjs');

class LoginFormStore {
  validationRules = {
    'email': 'required|email',
    'password': 'required',
  };
  form = {
    email: {
      value: '',
      error: ''
    },
    password: {
      value: '',
      error: ''
    },
    isValid: false
  }
  @action
  onFieldChange = (field, value) => {
    // update value and do a validation
    this.form.fields[field].value = value; // set a new value
    var validation = new Validator({
      email: this.from.email.value,
      password: this.from.email.value
    }, this.validationRules);
    this.form.meta.isValid = validation.passes();  // check if a form is valid
    this.form.fields[field].error = validation.errors.first(field)  // set an error if it exists
  };
}

model-shape.js

var loginFormModel = {
    fields: {
      email: {
        value: '', // binds to input value
        error: null, // shows beneif the input
      },
      password: {
        value: '',
        error: null,
      },
    },
    meta: {
      isValid: true, // is a 'submit' value disabled?
      error: null, // some generic error 
    },
  }

onFieldChange-updated.js

var onFieldChange = (field, value) => {
    this.form.fields[field].value = value; // set a new value
    var validation = new Validator(this.getValues(), this.validationRules);
    this.form.meta.isValid = validation.passes();  // check if a form is valid
    this.form.fields[field].error = validation.errors.first(field)  // set an error if it exist
};

validatorjs-example.js

var data = {
    name: 'John',
    email: 'not-valid-email'
};

var rules = {
    name: 'required',
    email: 'required|email'
};

var validation = new Validator(data, rules);

validation.passes(); // false
validation.errors.first('email'); // 'The email format is invalid.'