const allValid = [...this.template.querySelectorAll('lightning-input')].reduce((validSoFar, inputField) => {
            inputField.reportValidity();
            return validSoFar && inputField.checkValidity();
        }, true);

        if (allValid) {
            console.log('All fields are valid');
        } else {
            console.log('Please complete all required fields.');
        }