即使使用绝对URL，XMLHttpRequest也不会使用HTTPS

Question

我有以下代码和相关错误：

var xhttp = new XMLHttpRequest();
            xhttp.onreadystatechange = function () {
                if (this.readyState == 4 && this.status == 200) {
                    product_prices = this.responseText;
                }
            };
            xhttp.open("GET", ("https://example.com/" + products), true);
            xhttp.send();

chrome中的错误：

Mixed Content: The page at 'https://example.com' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'http://example.com/1_/'. This request has been blocked; the content must be served over HTTPS.

XHR failed loading: GET "http://example.com/1_/".

XHR failed loading: GET "https://example.com/1_/".

开发工具的网络部分还显示正确的https请求状态为：已取消

如果使用了相对网址，即使网页使用https，也会通过http发送请求。

服务器是django应用程序，SECURE_SSL_REDIRECT = True