如何从JS AJAX请求中获取PHP变量？

<?php
    $data = array(
        'var1' => 'value1',
        'var2' => 'value2'
    );

    echo json_encode($data);
?>

var xhr = new XMLHttpRequest();
xhr.open('GET', 'example.php', true);
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        var response = JSON.parse(xhr.responseText);
        var var1 = response.var1;
        var var2 = response.var2;
        
        // 在这里可以对获取到的变量进行操作
        console.log(var1);
        console.log(var2);
    }
};
xhr.send();