How can I get the title of a webpage given the url (an external url) using JQuery/JS

Something like this should work:

$.ajax({
  url: externalUrl,
  async: true,
  success: function(data) {
    var matches = data.match(/<title>(.*?)<\/title>/);
    alert(matches[0]);
  }   
});

TheSuperTramp is correct, above will not work if externalUrl is outside of your domain. Instead create this php file get_external_content.php:

<?php
function file_get_contents_curl($url){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    $data = curl_exec($ch);
    curl_close($ch);
    return $data;
}

$url = $_REQUEST["url"];
$html = file_get_contents_curl($url);

preg_match('/<title>(.+)<\/title>/',$html,$matches);
$title = $matches[1];

echo  json_encode(array("url" => $url, "title" => $title));

---

then in javascript:

function getTitle(externalUrl){
  var proxyurl = "http://localhost/get_external_content.php?url=" + externalUrl;
  $.ajax({
    url: proxyurl,
    async: true,
    success: function(response) {
      alert(response);
    },   
    error: function(e) {
      alert("error! " + e);
    }
  });
}