I m trying to scrape data from a website having multiple pages, the code works fine for a single run but when i try to put it in a loop, the website crashes and chrome says I m out of memory. Below is the javascript I m using :

// an XMLHttpRequest
var xhr = null;
var page = 1;
function scrape()
{
    // instantiate XMLHttpRequest object
    try
    {
        xhr = new XMLHttpRequest();
    }
    catch (e)
    {
        xhr = new ActiveXObject("Microsoft.XMLHTTP");
    }

    // handle old browsers
    if (xhr == null)
    {
        alert("Ajax not supported by your browser!");
        return;
    }

    // get city
    var city = document.getElementById("city").value;
    // get data
    xhr.onreadystatechange =
    function()
    {
        // only handle loaded requests
        if (xhr.readyState == 4)
        {
            if (xhr.status == 200)
            {
                    // insert link into DOM
                    some stuff
            }
            else
               alert("Error with Ajax call!");
        }
    }

        while(xhr.responseText != ""done) 
        {
            // construct URL
            var url = "scrape_data.php?city=" + city + "+" + page ;
            xhr.open("GET", url, true);
            xhr.send(null);
            page++;
        }
}

and this is the corresponding backend:

// get the q parameter 
preg_match('/.*(?=\+)/',$_GET["city"],$city);
preg_match('/(?<=\+).*/',$_GET["city"],$page);
// scrape data from shiksha.com
$string = @file_get_contents("http://www.shiksha.com/b-tech/colleges/b-tech-colleges-".urlencode($city)."-{$page}");
if($page === 1)
{
     // counting total number of pages
     preg_match_all('/class=" linkpagination">/',$string,$result);
     $GLOBALS["pages"] = sizeof($result[0]);
}

else $GLOBALS["pages"]--;

 // passing the string for scraping data  and storing in database

 if($GLOBALS["pages"]=== 0)
        print("loop");

now how do i loop through all the pages and also how do I check if all pages have been parsed (condition inside for loop). Thanks in advance for any help.