Modern, simple, lightweight (~5kb gzip) form validation library written in Typescript, with no dependencies (no JQuery!). Support a wide range of predefined rules (plus it's possible to define own custom rules), async validation, files validation, custom error messages and styles, localization.

NOTE

This is documentation for JustValidate 2. If you are looking for the old version, you could find it here.

Why JustValidate?

It's a right choice for you, if you have a site, a landing page without React, JQuery etc. and you want to quick, simple and powerful solution for validating your form.

Features

small size and zero dependencies
no need to change your HTML
a wide range of pre-defined rules
custom rules
custom styles and css classes for invalid fields and error messages
custom messages
showing tooltips as error messages
localization (defining error messages for different languages)
user-friendly setup: console warning messages if something incorrect
written in Typescript and good test coverage

Please, check out the examples https://just-validate.dev/examples/

Installation

npm

npm install just-validate --save

yarn

yarn add just-validate

And then use it as an imported module:

import JustValidate from 'just-validate';

const validate = new JustValidate('#form');

Or if you don't use module bundlers, just include JustValidate script on your page from CDN and call it as window.JustValidate:

<script src="https://unpkg.com/just-validate@latest/dist/just-validate.production.min.js"></script>
<body>
  <script>
    const validate = new window.JustValidate('#form');
  </script>
</body>

Predefined rules

There are plenty of rules which you could use out of the box:

required, non-empty fields
valid email address
min/max text length
valid number
min/max number
valid password
valid strong password
check for the custom regexp
min/max count of uploaded files
min/max size, types, extensions, names of uploaded files

Quick start

Let's say we have a basic HTML layout:

<form action="#" id="form" autocomplete="off">
  <label for="name">Enter your name</label>
  <input
    type="text"
    class="form__input form-control"
    placeholder="Enter your name"
    autocomplete="off"
    name="name"
    id="name"
  />
  <label for="email">Enter your email</label>
  <input
    type="email"
    class="form__input form-control"
    placeholder="Enter your email"
    autocomplete="off"
    name="email"
    id="email"
  />
  <button class="btn btn-primary" id="submit-btn">Submit</button>
</form>

Next, let's add JustValidate to our layout and define some simple rules.

First, we should create the instance new JustValidate('#form') by passing a form selector, or the element as an argument.

Second, we call .addField() with a field selector as the first argument and an array of rules as the second argument.

const validation = new JustValidate('#form');

validation
  .addField('#name', [
    {
      rule: 'minLength',
      value: 3,
    },
    {
      rule: 'maxLength',
      value: 30,
    },
  ])
  .addField('#email', [
    {
      rule: 'required',
      errorMessage: 'Email is required',
    },
    {
      rule: 'email',
      errorMessage: 'Email is invalid!',
    },
  ]);

And that's it! Now our form is validated!

More fields, group fields and rules

Let's check more advanced example:

<form action="#" id="form" autocomplete="off">
  <div class="row">
    <div class="col">
      <label for="name">Enter your name</label>
      <input
        type="text"
        class="form__input form-control"
        placeholder="Enter your name"
        autocomplete="off"
        name="name"
        id="name"
      />
    </div>
    <div class="col">
      <label for="email">Enter your email</label>
      <input
        type="email"
        class="form__input form-control"
        placeholder="Enter your email"
        autocomplete="off"
        name="email"
        id="email"
      />
    </div>
  </div>
  <div class="form-group mt-3">
    <label for="password">Enter your password</label>
    <input
      type="password"
      class="form__input form-control"
      placeholder="Enter your password"
      autocomplete="off"
      name="password"
      id="password"
    />
  </div>
  <div class="form-group mt-3">
    <label for="password">Repeat your password</label>
    <input
      type="password"
      class="form__input form-control"
      placeholder="Repeat your password"
      autocomplete="off"
      name="repeat-password"
      id="repeat-password"
    />
  </div>
  <div class="form-group mt-3">
    <label for="password">Enter your message</label>
    <textarea
      name="msg"
      cols="30"
      rows="10"
      class="form__textarea form-control"
      id="message"
    ></textarea>
  </div>
  <div class="form-group mt-4">
    <label for="favorite_animal_select" class="form-label"
      >Select you favorite animal</label
    >
    <select name="pets" id="favorite_animal_select" class="form-select">
      <option value="">--Please choose an option--</option>
      <option value="dog">Dog</option>
      <option value="cat">Cat</option>
      <option value="hamster">Hamster</option>
      <option value="parrot">Parrot</option>
      <option value="spider">Spider</option>
      <option value="goldfish">Goldfish</option>
    </select>
  </div>

  <div class="form-group mt-4">
    <div class="form-check">
      <label class="form-check-label" for="consent_checkbox"
        >I agree to provide the information</label
      >
      <input type="checkbox" id="consent_checkbox" class="form-check-input" />
    </div>
  </div>
  <div
    class="form-group mt-4"
    id="read_terms_checkbox_group"
    style="width: 250px"
  >
    <div class="form-check">
      <label class="form-check-label" for="read_terms_checkbox_group_1"
        >I have read Privacy Policy</label
      >
      <input
        type="checkbox"
        name="checkbox-group-fruit"
        id="read_terms_checkbox_group_1"
        class="form-check-input"
      />
    </div>
    <div class="form-check">
      <label class="form-check-label" for="read_terms_checkbox_group_2"
        >I have read Terms Of Use</label
      >
      <input
        type="checkbox"
        name="checkbox-group-fruit"
        id="read_terms_checkbox_group_2"
        class="form-check-input"
      />
    </div>
    <div class="form-check">
      <label class="form-check-label" for="read_terms_checkbox_group_3"
        >I have read Cookies Policy</label
      >
      <input
        type="checkbox"
        name="checkbox-group-fruit"
        id="read_terms_checkbox_group_3"
        class="form-check-input"
      />
    </div>
  </div>
  <div class="mt-4 form-group">
    <div class="pb-1">Please select the preferred way for communication</div>
    <div
      class="form-check"
      id="communication_radio_group"
      style="max-width: 200px"
    >
      <input
        type="radio"
        name="radio"
        class="form-check-input"
        id="communication_radio_group_1"
      />
      <label class="form-check-label" for="communication_radio_group_1">
        Email
      </label>
      <br />
      <input
        type="radio"
        name="radio"
        class="form-check-input"
        id="communication_radio_group_2"
      />
      <label class="form-check-label" for="communication_radio_group_2">
        SMS
      </label>
    </div>
  </div>

  <div class="d-grid mt-4">
    <button class="btn btn-primary" id="submit-btn">Submit</button>
  </div>
</form>

const validation = new JustValidate('#form', {
  errorFieldCssClass: 'is-invalid',
});

validation
  .addField('#name', [
    {
      rule: 'minLength',
      value: 3,
    },
    {
      rule: 'maxLength',
      value: 30,
    },
  ])
  .addField('#email', [
    {
      rule: 'required',
      errorMessage: 'Field is required',
    },
    {
      rule: 'email',
      errorMessage: 'Email is invalid!',
    },
  ])
  .addField('#password', [
    {
      rule: 'password',
    },
  ])
  .addField('#message', [
    {
      validator: (value) => {
        return value[0] === '!';
      },
    },
  ])
  .addField('#consent_checkbox', [
    {
      rule: 'required',
    },
  ])
  .addField('#favorite_animal_select', [
    {
      rule: 'required',
    },
  ])
  .addRequiredGroup(
    '#read_terms_checkbox_group',
    'You should select at least one communication channel'
  )
  .addRequiredGroup('#communication_radio_group')
  .onSuccess((event) => {
    console.log('Validation passes and form submitted', event);
  });

Instance setting

new JustValidate(
   form: string | Element,
   globalConfig?: {
     errorFieldStyle: Partial<CSSStyleDeclaration>,
     errorFieldCssClass: string,
     errorLabelStyle: Partial<CSSStyleDeclaration>,
     errorLabelCssClass: string,
     lockForm: boolean,
     testingMode: boolean,
     focusInvalidField?: boolean,
     tooltip?: {
       position: 'left' | 'top' | 'right' | 'bottom',
     },
   },
   dictLocale?: {
     key: string;
     dict: {
       [localeKey: string]: string,
     };
   }[];
);

For example, full setting:

const validation = new JustValidate(
  '#form',
  {
    errorFieldCssClass: 'is-invalid',
    errorFieldStyle: {
      border: '1px solid red',
    },
    errorLabelCssClass: 'is-label-invalid',
    errorLabelStyle: {
      color: 'red',
      textDecoration: 'underlined',
    },
    focusInvalidField: true,
    lockForm: true,
    tooltip: {
      position: 'top',
    },
  },
  [
    {
      key: 'Name is too short',
      dict: {
        ru: 'Имя слишком короткое',
        es: 'El nombre es muy corto',
      },
    },
    {
      key: 'Field is required',
      dict: {
        ru: 'Обязательное поле',
        es: 'Se requiere campo',
      },
    },
  ]
);

lockForm - if true, lock form during validation. Could be useful for async validation to make it impossible for user to interact with the form
focusInvalidField - if true, the first invalid field will be focused after the form submitting
tooltip if the field defined, tooltips will be displayed instead of regular error labels. It has position field which could be 'left' | 'top' | 'right' | 'bottom'
localization object will be explained in Localization section

Methods

Define validation rules for the new field:

.addField(
  field: string,
  rules: {
    rule?: Rules;
    errorMessage?: string;
    validator?: (
      value: string | boolean,
      context: FieldsInterface
    ) => boolean | (() => Promise<boolean>);
    value?: number | string | RegExp;
  },
  config?: {
    errorFieldStyle: Partial<CSSStyleDeclaration>;
    errorFieldCssClass: string;
    errorLabelStyle: Partial<CSSStyleDeclaration>;
    errorLabelCssClass: string;
    tooltip?: {
      position: 'left' | 'top' | 'right' | 'bottom';
    };
  }
)

Make the new group field required. It could be a group of checkboxes or radio buttons.

It means that at least one input in the group should be checked/selected.

.addRequiredGroup(
    groupField: string,
    errorMessage?: string,
    config?: {
      errorFieldStyle: Partial<CSSStyleDeclaration>;
      errorFieldCssClass: string;
      errorLabelStyle: Partial<CSSStyleDeclaration>;
      errorLabelCssClass: string;
      tooltip?: {
        position: 'left' | 'top' | 'right' | 'bottom';
      };
    }
)

.onSuccess(event) - callback if validation success

.onFail(fields) - callback if validation failed

Rule object

{
  rule: String,
  errorMessage: String,
  validator: (
    value: String | Boolean,
    context: Object
 ) => Boolean | Promise;
 value: number | string;
}

Field rule could be one of these values:

required - Required field, not empty
email - Valid email address
minLength - Limit the minimum text length
maxLength - Limit the maximum text length
number - Value should be a number
minNumber - Number should be more than defined value
maxNumber - Number should be less than defined value
password - Minimum eight characters, at least one letter and one number
strongPassword - Minimum eight characters, at least one uppercase letter, one lowercase letter, one number and one special character
customRegexp - Custom regexp expression
minFilesCount - Uploaded files count should be more than defined value
maxFilesCount - Uploaded files count should be less than defined value
files - Uploaded files attributes should be valid, based on value config (check details below in Files validation section)

Field errorMessage used for customizing the error message for this rule.

Field value used only with minLength, maxLength, minNumber, maxNumber, customRegexp rules to define the rule value, for example:

validation.addField('#name', [
  {
    rule: 'minLength',
    value: 3,
  },
]);

validation.addField('#password', [
  {
    rule: 'customRegexp',
    value: /(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@$!%*#?&^_-]).{8,}/,
  },
]);

Field validator used for custom validation. It should return a boolean or a function which returns a Promise.

validation.addField('#text', [
  {
    validator: (value) => value[value.length - 1] === '.',
  },
]);

validation.addField('#email', [
  {
    validator: (value) => () => {
      return new Promise((resolve) => {
        setTimeout(() => {
          resolve(true);
        }, 500);
      });
    },
  },
]);

Also, it's possible to do validation based on other fields:

validation.addField('#repeat-password', [
  {
    validator: (value, fields) => {
      if (fields['#password'] && fields['#password'].elem) {
        const repeatPasswordValue = fields['#password'].elem.value;

        return value === repeatPasswordValue;
      }

      return true;
    },
    errorMessage: 'Passwords should be the same',
  },
]);

Files validation

It's possible to validate min/max count of uploaded files and check for type, extension, min/max size and name of uploaded files.

Uploaded files count

<input type="file" name="file" id="file" multiple />

validation.addField('#file', [
  {
    rule: 'minFilesCount',
    value: 1,
  },
  {
    rule: 'maxFilesCount',
    value: 3,
  },
]);

Files attributes validation

validation.addField('#file', [
  {
    rule: 'files',
    value: {
      files: {
        extensions: ['jpeg', 'png'],
        maxSize: 25000,
        minSize: 1000,
        types: ['image/jpeg', 'image/png'],
        names: ['file1.jpeg', 'file2.png'],
      },
    },
  },
]);

Format of value for files rule:

{
  files: {
    extensions?: string[];
    types?: string[];
    minSize?: number;
    maxSize?: number;
    names?: string[];
  }
}

minSize and maxSize should be defined in bytes.

Localization

You could define your own translations for different languages. To do that you should define dictLocale array, like:

  [
    {
      key: 'Name is too short',
      dict: {
        ru: 'Имя слишком короткое',
        es: 'El nombre es muy corto',
      },
    },
    {
      key: 'Field is required',
      dict: {
        ru: 'Обязательное поле',
        es: 'Se requiere campo',
      },
    },
  ]

Field key should be defined as a key string, which also should be defined as errorMessage in a rule object.

dict should be an object with languages keys with their translations.

To switch a language you should call validation.setCurrentLocale('ru');. The argument for setCurrentLocale() method you should pass the key, which you defined in dict object, or you could call with empty argument to set the default language (strings defined in key fields).

document.querySelector('#change-lang-btn-en').addEventListener('click', () => {
  validation.setCurrentLocale();
});

document.querySelector('#change-lang-btn-ru').addEventListener('click', () => {
  validation.setCurrentLocale('ru');
});

document.querySelector('#change-lang-btn-es').addEventListener('click', () => {
  validation.setCurrentLocale('es');
});

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

README.md

README.md

Why JustValidate?

Features

Installation

npm

yarn

Predefined rules

Quick start

More fields, group fields and rules

Instance setting

Methods

Rule object

Files validation

Uploaded files count

Files attributes validation

Localization

Files

README.md

Latest commit

History

README.md

File metadata and controls

Why JustValidate?

Features

Installation

npm

yarn

Predefined rules

Quick start

More fields, group fields and rules

Instance setting

Methods

Rule object

Files validation

Uploaded files count

Files attributes validation

Localization