In JavaScript form validation, how can the return value of a function be used to prevent form submission until all checkboxes are selected?

To prevent form submission until all checkboxes are selected, you can create a JavaScript function that checks if all checkboxes are checked when the form is submitted. If any checkbox is not checked, the function should return false to prevent the form submission. This can be achieved by attaching the function to the form's onsubmit event. ```javascript function validateForm() { var checkboxes = document.querySelectorAll('input[type="checkbox"]'); for (var i = 0; i < checkboxes.length; i++) { if (!checkboxes[i].checked) { alert('Please select all checkboxes'); return false; } } return true; } document.getElementById('myForm').onsubmit = validateForm; ```