Magento2 Checkout Page – Validation Error in Shipping Address

You can simply create your own element with modified validation process for this purpose. In your extension create a new file view/base/web/js/form/element/custom.js with the following content:

define([
    'Magento_Ui/js/form/element/abstract',
    'Magento_Ui/js/lib/validation/validator'
], function (Abstract, validator) {
    'use strict';

    return Abstract.extend({
        validate: function () {
            var value   = this.value(),
                result  = validator(this.validation, value, this.validationParams),
                message = result.message,
                isValid = result.passed;

            this.error(message);
            this.bubble('error', message);

            if (!isValid) {
                this.source.set('params.invalid', true);
                alert('Please, specify a delivery date');
            }

            return {
                valid: isValid,
                target: this
            };
        }
    });
});

Then, in LayoutProcessorPlugin change the 'component' value to the newly created element:

'component' => 'Modules_Deliverydate/js/form/element/custom'

In that way, you are able to extend the Abstract element and modify the "validate" method by removing field visibility checking etc. In this example the error message is being shown as an alert but you can use whatever you want. Hope it will help.

$(".check_item").change(function() {
    if(this.checked) {
        //Do stuff
    }
});