np# Form Validation Library

This is a javascript utility for setting up client-side form validation. It makes use of the Constrain Validation API and the associated HTML attributes, It provides a custom error message using the elements eds-c-error component

Custom error messages and custom validation functions can be specified using data attributes

To set up validation import the library and set up a configuration object with custom values:

import createValidatorLibrary from '@springernature/form-validation';

const validator = createValidatorLibrary({
    errorMessages: { required: 'This field is required.' },
    errorTemplateSelector: '#error-message-template'
});

To add client side validation to all forms on the page include the following on document ready:

validator.trackAndValidateForms();

Configuration values

errorTemplateSelector: Here you can define a selector for your error messages.

errorMessages: custom error messages for the following HTML validation types: required, minimumLength, maximumLength, badInput, typeMismatch. Here you can also add error messages for any custom validation functions you have added or the two custom validation functions included with the library: 'forbidTrailingWhitespace' and 'isEqualToField'.

customValidators: This defines custom validation function, the name must match with a data attribute and a custom error message defined in 'errorMessages'.

For example:

const validator = createValidatorLibrary({
    errorTemplateSelector: '#error-message-template',
    errorMessages: {
        isDoiStartsWithTen: 'Your DOI must begin with 10',
        isValidDoi: 'Your DOI must be in correct syntax'
        },
        customValidators: {
            isDoiStartsWithTen: (input) => {
                const doiPattern = /^10/;
                return doiPattern.test(input.value);
            },
            isValidDoi: (input) =>  {
                const doiPattern = /^10.\d{4,9}\/[-._;()/:A-Z0-9]+$/i;
                return doiPattern.test(input.value);
            }
        });

A custom data attribute should then be added to any form input that you wish to validate against this custom function so for the example above:

<input type="text" value="" data-validation-is-doi-starts-with-ten data-validation-is-valid-doi> </input>