如何使用js或jQuery向ajax请求添加自定义HTTP标头？

var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.example.com/data', true);

xhr.onreadystatechange = function() {
    if (xhr.readyState == 4 && xhr.status == 200) {
        console.log(xhr.responseText);
    }
};

xhr.setRequestHeader('Custom-Header', 'CustomHeaderValue');
xhr.send();

$.ajax({
    url: 'https://api.example.com/data',
    type: 'GET',
    beforeSend: function(xhr) {
        xhr.setRequestHeader('Custom-Header', 'CustomHeaderValue');
    },
    success: function(data) {
        console.log(data);
    }
});