10.js

function shiftSelect() {
    const checkboxes = document.querySelectorAll(
        ".inbox input[type = 'checkbox"
    );

    let lastChecked;
    let inBetween = false;
    function handleCheck(e) {
        if (e.shiftKey && this.checked) {
            checkboxes.forEach((checkbox) => {
                if (checkbox === this || checkbox === lastChecked) {
                    inBetween = !inBetween;
                }
                if (inBetween) {
                    checkbox.checked = true;
                }
            });
        }
        lastChecked = this;
    }
    checkboxes.forEach((checkbox) =>
        checkbox.addEventListener("click", handleCheck)
    );
}

window.addEventListener("DOMContentLoaded", shiftSelect);