Lightweight (~4,5kb gzip) form validation in Javascript Vanilla, without dependencies, with customizable rules (including remote validation), customizable messages and customizable submit form with ajax helper.

Demo:
Classic validation https://horprogs.github.io/Just-validate/
Classic validation with tooltips https://horprogs.github.io/Just-validate/tooltip.html

npm install just-validate --save

yarn add just-validate

Include the script of the Just-validate on your page

<script src="./path/to/just-validate.min.js"></script>
...
</body>

<form action="#" class="js-form form">
    <div class="row">
      <div class="form-group col-md-6">
        <label for="name">Enter your name</label>
        <input type="text" class="form__input form-control" placeholder="Enter your name" autocomplete="off" data-validate-field="name" name="name" id="name">
      </div>
      <div class="form-group col-md-6">
        <label for="email">Enter your email</label>
        <input type="email" class="form__input form-control" placeholder="Enter your email" autocomplete="off" data-validate-field="email" name="email" id="email">
      </div>
    </div>
    <div class="form-group">
      <label for="password">Enter your password</label>
      <input type="password" class="form__input form-control" placeholder="Enter your password" autocomplete="off" data-validate-field="password" name="password" id="password">
    </div>
    <div class="form-group">
      <label for="password">Enter your text</label>
      <textarea name="msg" cols="30" rows="10" class="form__textarea form-control" data-validate-field="text" id="text"></textarea>
    </div>
    <div class="form-group">
      <input type="checkbox" id="checkbox" class="form__checkbox" data-validate-field="checkbox" checked><label for="checkbox">I agree</label>
    </div>
    <div class="form-group">
      <label><input type="checkbox" class="form__checkbox" data-validate-field="checkbox2" checked>I agree</label>
    </div>
    <div class="form-group">
      <label><input type="radio" name="radio" class="form__radio" data-validate-field="radio">Male</label>
      <br>
      <label><input type="radio" name="radio" class="form__radio" data-validate-field="radio">Female</label>
    </div>
    <button class="form__btn btn btn-primary">SUBMIT</button>
  </form>

data-validate-field : Name of field to which the rule will be applied

Plugin has default fields, which already have rules.

Field: email

• required
• email
• remote

Field: name

• required
• minLength: 3
• maxLength: 15

Field: text

• required
• minLength: 5
• maxLength: 300

Field: password

• required
• password (at least 1 digit and 1 letter)
• minLength: 4
• maxLength: 8

Field: zip

• required
• zip (4-5 digits)

Field: phone

• phone (format 111-222-3333)

You can create your own fields, e.g. data-validate-field="myField".

• required - Required field, not empty
• email - Check a valid email address
• minLength - Limit the minimum value
• maxLength - Limit the maximum value
• password - At least 1 letter and 1 digit
• zip - 4-5 digits
• phone - Format 111-222-3333
• remote - validate value via remote api
• strength - validate field for default or custom regexp
• function - provide your own validation function

More about remote rule: Rule check remote server api for correct answer. For example:

remote: {
    url: '/check-correct',
    successAnswer: 'OK',
    sendParam: 'email',
    method: 'GET'
}

• url - remote server api url
• successAnswer - expected response from server, if value is correct
• sendParam - parameter to be sent to server
• method - GET or POST

More about function rule: Provide a function which takes two arguments name and value and returns true or false

• name - the name of the element
• value - the value of the element

The following example will only validate input of a field if it is "hi"

function: (name, value) => {
    return (name === 'hi');
}

Strength rule format: Default (at least one uppercase letter, one lowercase letter and one number):

strength: {
    default: true
}

Custom (use your own regexp for check):

strength: {
    custom: '^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]'
}

new window.JustValidate(element, options);

• element - string, selector of DOM element
• options - object

Initiate plugin:

First argument - selector of DOM element.

new window.JustValidate('.js-form');

In this case default rules and messages will be applied.

Also, you can customize validation:

new JustValidate('.js-form', {
    rules: {
      checkbox: {
        required: true
      },
      myField: {
        required: true
      },
      email: {
        required: false,
        email: true
      },
      password: {
        strength: {
          default: true,
        }
    },
    messages: {
      name: {
        minLength: 'My custom message about only minLength rule'
      },
      email: 'My custom message about error (one error message for all rules)'
    },

    submitHandler: function (form, values, ajax) {

      ajax({
        url: 'https://just-validate-api.herokuapp.com/submit',
        method: 'POST',
        data: values,
        async: true,
        callback: function(response)  {
          console.log(response)
        }
      });
    },
  });

You can override custom message for once rule or for all at once rules.

Also, you can validate for required radiobuttons. For this, you need to create input[type="radio"] fields with identical data-validate-field (it's important).

You can override standard submit form, using method submitHandler. It has 3 arguments:

• form - DOM link to form
• values - object of fields values
• ajax - function of XMLHttpRequest

Function ajax helps you to send XMLHTTPRequest.

Format:

ajax({
    url: 'https://just-validate-api.herokuapp.com/submit',
    method: 'POST',
    data: values,
    async: true,
    callback: function(response)  {
      console.log(response)
    }
});

There is a property focusWrongField (default false), which turns on focusing on the first incorrect input after submit.

There is a method invalidFormCallback, which runs when validation failed. It takes one argument: object with errors messages.

You can show errors in the form of tooltips.

To do this, connect the file styles dist/css/justValidateTooltip.css or dist/css/justValidateTooltip.min.css on page.

<link rel="stylesheet" href="./path/to/justValidateTooltip.min.css">

For a container inside of which input, add a class just-validate-tooltip-container or add our class

 <div class="form-group col-md-6">
    <label for="name">Enter your name</label>
    <div class="just-validate-tooltip-container">
        <input type="text" class="form__input form-control" placeholder="Enter your name" data-validate-field="name">
    </div>
 </div>

You can customize time show of error, using property fadeOutTime, for example:

new window.JustValidate('.js-form', {
    tooltip: {
        fadeOutTime: 4000 // default value - 5000 
    }
});

You can customize class hide of tooltip, using property fadeOutClass, for example:

new window.JustValidate('.js-form', {
    tooltip: {
        fadeOutClass: '.hide' // default value - just-validate-tooltip-hide
    }
});

You can customize class inside of which input, using property selectorWrap, for example:

new window.JustValidate('.js-form', {
    tooltip: {
        selectorWrap: '.tooltip-wrapper' // default value - just-validate-tooltip-container
    }
});

You can customize style color of error, using property colorWrong, for example:

new window.JustValidate('.js-form', {
    colorWrong: 'red'
});

Error fields and messages have classes: js-validate-error-label and js-validate-error-field

new window.JustValidate('.js-form-1', {
    rules: {
        email: {
            email: true,
            remote: {
                url: 'https://just-validate-api.herokuapp.com/check-correct',
                sendParam: 'email',
                successAnswer: 'OK',
                method: 'GET'
            }
        },
        login: {
            remote: {
                url: 'https://just-validate-api.herokuapp.com/check-correct',
                sendParam: 'login',
                successAnswer: 'OK',
                method: 'GET'
            }
        }
    },
    messages: {
        email: {
            remote: 'Email already exist',
            email: 'Email not valid!'
        },
        login: {
            remote: 'Login already exist',
            required: 'Login is required!'
        }
    },
});

new window.JustValidate('.js-form', {
    rules: {
        checkbox: {
            required: true
        },
        checkbox2: {
            required: true
        },
        email: {
            required: true,
            email: true,
        }
    },
    
    focusWrongField: true,

    submitHandler: function (form, values, ajax) {
        ajax({
            url: 'https://just-validate-api.herokuapp.com/submit',
            method: 'POST',
            data: values,
            async: true,
            callback: function (response) {
                alert('AJAX submit successful! \nResponse from server:' + response)
            },
            error: function (response) {
                alert('AJAX submit error! \nResponse from server:' + response)
            }
        });
    },
    
    invalidFormCallback: function (errors) {
    		console.log(errors);
    },
});

Added rule for check strength of password (default and custom)

Added tooltip style error

Added feature for check required radio buttons

Added feature to allow the user to provide their own validation function

Added feature for focus incorrect field after validation Added callback, when validation failed

* Check the open issues or open a new issue to start a discussion around your feature idea or the bug you found.
* Fork repository, make changes, add your name and link in the authors session readme.md
* Send a pull request

Thank you