我可以将信息从浏览器控制台（通过AJAX）发送到本地/远程主机上的php文件吗？

For example: Stackoverflow's page

I push F12 in Crome web-browser and in console put next:

var item = document.querySelectorAll('.question-summary');
var outputValue = item.length;
outputValue;

The output I get is 15

Question is can I send this info (the output value) to my myfile.php file (for example get sing in one of my divs There are 15 questions on that particular stackoverflow's page via <? echo 'There are ' . outputValue . ' questions on that particular stackoverflow's page'; ?>), so in future I'll be able to put this information to MySQL database (but for now I just need to print out outputValue on myfile.php )?

Yes, using a GET request, you could pass the length as a query string parameter -

xmlhttp=new XMLHttpRequest();
xmlhttp.open("GET", "server.php?question-summaries="+item.length);
xmlhttp.send();

server.php

if (is_numeric($_GET['question-summaries'])) {
    // Insert into database
}