Add custom validations before order placement

What's in this topic

This topic describes how to add custom validations to be performed before the order is placed during checkout. Namely, the validations which are performed after a shopper clicks the Place Order button. Writing the validation logic itself is not covered in this topic.

Overview

To add custom validations before the order placement action, you must do the following:

Create the validator.
Add validator to the validators pool.
Declare the validation in the checkout layout.

Create the validator

For the sake of compatibility, upgradability and easy maintenance, do not edit the default Magento code, add your customizations in a separate module. For your checkout customization to be applied correctly, your custom module should depend on the Magento_Checkout module. Do not use Ui for your custom module name, because %Vendor%_Ui notation, required when specifying paths, might cause issues.

In your custom module directory, create a .js file implementing the validator. It should be located under <your_module_dir>/view/frontend/web/js/model directory.

Following is a sample of the validator .js file. It must necessarily implement the validate() method:

define(
    [],
    function () {
        'use strict';
        return {
            /**
             * Validate something
             *
             * @returns {boolean}
             */
            validate: function() {
                //Put your validation logic here
                return true;
            }
        }
    }
);

Add validator to the validators pool

Your custom validator must be added to the pool of “additional validators”. To do this, in the <your_module_dir>/view/frontend/web/js/view directory create a new <your-validation>.js file with the following content:

define(
    [
        'uiComponent',
        'Magento_Checkout/js/model/payment/additional-validators',
        '<your_module>/js/model/your-validator'
    ],
    function (Component, additionalValidators, yourValidator) {
        'use strict';
        additionalValidators.registerValidator(yourValidator);
        return Component.extend({});
    }
);

Declare the validation in the checkout layout

In your custom module directory, create a new <your_module_dir>/view/frontend/layout/checkout_index_index.xml file. In this file, add the following:

<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
<referenceBlock name="checkout.root">
    <arguments>
        <argument name="jsLayout" xsi:type="array">
            <item name="components" xsi:type="array">
                <item name="checkout" xsi:type="array">
                    <item name="children" xsi:type="array">
                        <item name="steps" xsi:type="array">
                            <item name="children" xsi:type="array">
                                <item name="billing-step" xsi:type="array">
                                    <item name="children" xsi:type="array">
                                        <item name="payment" xsi:type="array">
                                            <item name="children" xsi:type="array">
                                                <item name="additional-payment-validators" xsi:type="array">
                                                    <item name="children" xsi:type="array">
                                                        <!-- Declare your validation. START -->
                                                        <item name="your-validator" xsi:type="array">
                                                            <item name="component" xsi:type="string">%your_module_dir%/js/view/%your-validation%</item>
                                                        </item>
                                                        <!-- Declare your validation. END -->
                                                    </item>
                                                </item>
                                            </item>
                                        </item>
                                    </item>
                                </item>
                            </item>
                        </item>
                    </item>
                </item>
            </item>
        </argument>
    </arguments>
</referenceBlock>
    </body>
</page>

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