vue3-form-validation

Form validation for Vue 3

Easy to use opinionated Form validation for Vue 3.

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

npm i 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.

useValidation

const { form, add, remove, onSubmit } = useValidation<T>(formData)

• useValidation takes the following parameters:

Parameters	Type	Required	Description
formData	object	true	The structure of your Form data.

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 type definition looks like the following:

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

To get the best IntelliSense while writing the useValidation function, it's recommended to define the structure of your formData upfront and pass it as the generic parameter T. If at some point the provided type does not fit the required structure, it will let you know by converting that section to be of type never. Please note that when writing in a normal .js file, the type will often result in never even though the structure of the input might be correct. This is definitely not ideal and can probably be changed, but type inference can be a bit tricky sometimes. 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:

State	Type	Description
form	object	Transformed formData object with added metadata to every Form Field.

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

Typing:

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.

Key	Value	Description
uid	number	Unique identifier of the Form Field. For dynamic Forms this can be used as the key attribute in v-for.
value	T	The modelValue of the Form Field which is meant to be used together with v-model.
errors	string[]	Array of validation error messages.
validating	boolean	True while atleast one rule is validating.
onBlur	function	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:

Signature	Parameters	Description
onSubmit(success, error?)		Function that will validate all Form Fields. It takes two parameters, a success callback and an optional error callback.
	success	Will be called if there are no validation errors. Receives the formData as it's first argument.
	error?	Will be called if there are validation errors. Receives no arguments.
add(pathToArray, value)		Utility function for writing dynamic Forms. It takes two parameters, a pathToArray of type (string | number)[] and a value.
	pathToArray	Tupel of string and numbers 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, index)		Identical to add but instead of providing a value you provide an index that will be removed.

At the moment, there is no good IntelliSense support for the add and remove methods. When TypeScript 4.1 will be released and Vue supports it, this can be changed however. Also if you want to take a look at some more examples, you can clone this repository to your local machine and run npm run dev, which will start a development server with an example site.

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.

main/Form.ts

// Somewhere at the bottom of the file

let error: unknown;
// ...
error = await rule(formField.modelValue);
// ...
if (typeof error === 'string') {
  // report validation error
}
// ...

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 already 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);
  })