var formsjsForm = new formsjs.Form();
formsjsForm.formData = { // Input fields should read/write data to this object.
  username: "bvaughn"    // Default values can be provided.
};
formsjsForm.validationService = { // Maps field-names to validation rules.
  username: {                     // It should mirror the structure of form-data.
    required: true,
    type: "string"
  }
};
formsjsForm.submitFunction = function() {
  // You provide this function.
  // It is responsible for submitting your form data and returning a Promise.
  // This Promise should resolve/reject based on the response you receive after submitting.
};

var attributeMetadata = formsjsForm.registerAttribute('username');

// AttributeMetadata defines an errorMessages Array.
// You should bind to it in your view as it is used to show validation errors.
attributeMetadata.errorMessages;

// AttributeMetadata exposes a method named validate().
// You should call it any time your view updates the field's value.
// It will (asynchronously) update the 'errorMessages' property.
attributeMetadata.validate();

var formElement = document.getElementById('yourForm');

// Angular/jQuery style
$(formElement).on("submit", function() {
  formsjsForm.submitIfValid();

  return false;
});

// Plain JavaScript
formElement.addEventListener("submit", function() {
  event.preventDefault();

  formsjsForm.submitIfValid();
}), false);