vue3-form-validation

Form Validation for Vue 3

Opinionated Vue composition function for Form Validation.

• :milky_way: Written in TypeScript
• :ocean: Dynamic Form support
• :fallen_leaf: Light weight

npm install vue3-form-validation

Validation is async and is utilising Promise.allSettled, which has not yet reached cross-browser stability. Example usage can be found in this Code Sandbox.

API

This package exports one function useValidation, plus some type definitions for when using TypeScript.

const {
  form,
  errors,
  submitting,
  validateFields,
  resetFields,
  add,
  remove
} = useValidation<T>(formData);

useValidation takes the following parameters:

• formData
  • Type - object
  • Required - true
  • Description - The structure of your formData.

The formData object has a structure that is similar to any other object you would write for v-model data binding. The only difference being that together with every value you can provide rules to display validation errors.

Let's look at an example how the structure of some formData object can be converted to an object with the addition of rules:

const formData = {
  name: '',
  email: '',
  password: ''
};

// The above can be converted to the following
const formDataWithRules = {
  name: {
    $value: '',
    $rules: [name => !name && 'Name is required']
  },
  email: {
    $value: '',
    $rules: [email => !email && 'E-Mail is required']
  },
  password: {
    $value: '',
    $rules: [
      pw => pw.length > 7 || 'Password has to be longer than 7 characters'
    ]
  }
};

The formData object can contain arrays and can be deeply nested. At the leaf level, the object should contain Form Fields whose simplified type definition looks like the following:

type Field<T> = {
  $value: Ref<T> | T;
  $rules?: Rule<T>[];
};

To get better type inference while writing the useValidation function, it's recommended to define the structure of your formData upfront and pass it as the generic parameter T. The type for the example above is pretty straightforward:

type FormData = {
  name: Field<string>;
  email: Field<string>;
  password: Field<string>;
};

useValidation exposes the following state:

• form
  • Type - object
  • Description - Transformed formData object.
• submitting
  • Type - Ref<boolean>
  • Description - True during validation after calling validateFields.
• errors
  • Type - ComputedRef<string[]>
  • Description - Array of all current validation error messages.

Form is a reactive object with identical structure as the formData input, but with added metadata to every Form Field.

type TransformedField<T> = {
  $uid: number;
  $value: T;
  $errors: string[];
  $validating: boolean;
  $onBlur(): void;
};

// The type of form in the example above would therefore be
const form: {
  name: TransformedField<string>;
  email: TransformedField<string>;
  password: TransformedField<string>;
};

As you may have noticed, all of the properties are prefixed with the $ symbol, which is to distinguish them from other properties but also to avoid naming conflicts.

• $uid
  • Type - number
  • Description - Unique identifier of the Form Field. For dynamic Forms this can be used as the key attribute in v-for.
• $value
  • Type - T
  • Description - The modelValue of the Form Field which is meant to be used together with v-model.
• $errors
  • Type - string[]
  • Description - Array of validation error messages.
• $validating
  • Type - boolean
  • Description - True while at least one rule is validating.
• $onBlur
  • Type - function
  • Description - Function which will mark this Form Field as touched. When a Form Field has been touched it will validate all it's rules after every input. Before it will not do any validation.

useValidation exposes the following methods:

• validateFields() -> Promise
  • Description - Validate all Form Fields.
  • Returns - A Promise which will reject if there are validation errors, and resolve with the formData otherwise.
• resetFields() -> void
  • Description - Reset all Form Fields to their original values.
• add(pathToArray: (string | number)[], value: any) -> void
  • Description - Utility function for writing dynamic Forms.
  • Parameters
    • pathToArray - Tuple representing the path to an array in the formData.
    • value - The value that will be pushed to the array at the given path.
• remove(pathToArray: (string | number)[], index: number) -> void
  • Description - Utility function for writing dynamic Forms.
  • Parameters
    • pathToArray - Tuple representing the path to an array in the formData.
    • index - Array index that will be remove.

Writing Rules

Rules are functions that should return a string when the validation fails. They can be written purely as a function or together with a key property in an object. They can also alternatively return a Promise when you have a rule that requires asynchronous code.

Typing:

type SimpleRule<T = any> = (value: T) => Promise<unknown> | unknown;
type KeyedRule<T = any> = { key: string; rule: SimpleRule<T> };
type Rule<T = any> = SimpleRule<T> | KeyedRule<T>;

Keyed rules that share the same key will be executed together, this can be useful in a situation where rules are dependent on another. For example the Password and Repeat Password fields in a Login Form. Rules will always be called with the latest modelValue, to determine if a call should result in an error, it will check if the rule's return value is of type string. This allows you to write many rules in one line:

const required = value => !value && 'This field is required';
const min = value =>
  value.length > 3 || 'This field has to be longer than 3 characters';
const max = value =>
  value.length < 7 || 'This field is too long (maximum is 6 characters)';

Async rules allow you to perform network requests, for example checking if a username exists in the database:

const isNameTaken = name =>
  new Promise(resolve => {
    setTimeout(() => {
      if (['foo', 'bar'].includes(name)) {
        resolve();
      } else {
        resolve('This name is already taken');
      }
    }, 2000);
  });

Contributing

Contributing

License

MIT