Form validation for Vue 3

Easy to use opinionated Form validation for Vue 3.

• 🌌 Written in TypeScript
• 🌊 Dynamic Form support
• 🍂 Light weight

npm i vue3-form-validation

Validation is async and is utilising Promise.allSettled, which has not yet reached cross-browser stability.

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:

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 for 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 either be flat or nested by using arrays. The type definition for some Form field 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 paramter. If at some point the provided type does not fit the required structure, it will let you know by converting the problematic part to be of type never. The type for the example above is pretty straightforward:

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

• useValidation exposes the following state:

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 be
const form: {
  name: TransformedField<string>;
  email: TransformedField<string>;
  password: TransformedField<string>;
}

• useValidation exposes the following methods:

At the time there is no good IntelliSense support for the add and remove functions. When TypeScript 4.1 will be released and Vue supports it, this can be changed however. Also there are currently no online usage examples, you can however 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

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

Of course you can also return a Promise directly or perform network requests, for example checking if a username already exists in the database.