js 获取页面控件的值吗

// 假设有一个ID为 'username' 的文本框
let username = document.getElementById('username').value;
console.log(username);

// 假设有一个ID为 'country' 的下拉列表
let selectedCountry = document.getElementById('country').value;
console.log(selectedCountry);

let radioButtons = document.getElementsByName('gender');
let gender;
for (let i = 0; i < radioButtons.length; i++) {
    if (radioButtons[i].checked) {
        gender = radioButtons[i].value;
        break;
    }
}
console.log(gender);

let checkboxes = document.getElementsByName('interests');
let interests = [];
for (let i = 0; i < checkboxes.length; i++) {
    if (checkboxes[i].checked) {
        interests.push(checkboxes[i].value);
    }
}
console.log(interests);

window.onload = function() {
    let username = document.getElementById('username').value;
    console.log(username);
};