In Magento 2, we can add the custom validation rules by creating a Javascript mixin for the mage/validation module and calling the $.validator.addMethod function with the custom validation rule parameters as described below:
Syntax To Create New Validation Rule:
$.validator.addMethod(
'custom-rule-name',
function(value, element) {
// You need to return true or false after validation rule check
},
$.mage.__('Add error message here to display if validation fails')
)
Following is the code snippet which adds a simple new validation rule to the mixin to validate if an input field has only four words.
Path: app/code/Vendor/Module/view/frontend/requirejs-config.js
var config = {
config: {
mixins: {
'mage/validation': {
'Vendor_Module/js/custom-validation-mixin': true
}
}
}
}
Path: app/code/Vendor/Module/view/frontend/web/js/custom-validation-mixin.js
define(['jquery'], function($) {
'use strict';
return function() {
$.validator.addMethod(
'validate-four-words',
function(value, element) {
return value.split(' ').length == 4;
},
$.mage.__('Please enter exactly four words')
)
}
});
Hope this helps !