JavaScript/jQuery check broken links

Question

I developed a small Javascript/jQuery program to access a collection of pdf files for internal use. And I wanted to have the information div of a pdf file highlighted if the file actually exist.

Is there a way to programmatically determine if a link to a file is broken? If so, How?

Any guide or suggestion is appropriated.

Answer 1

If the files are on the same domain, then you can use AJAX to test for their existence as Alex Sexton said; however, you should not use the GET method, just HEAD and then check the HTTP status for the expect value (200, or just less than 400).

Here's a simple method provided from a related question:

function urlExists(url, callback) {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
      callback(xhr.status < 400);
    }
  };
  xhr.open('HEAD', url);
  xhr.send();
}

urlExists(someUrl, function(exists) {
    console.log('"%s" exists?', someUrl, exists);
});

Answer 2

Issue is that JavaScript has the same origin policy so you can not grab content from another domain. This won't change by upvoting it (wondering about the 17 votes). I think you need it for external links, so it is impossible just with .js ...

Answer 3

If the files are not on an external website, you could try making an ajax request for each file. If it comes back as a failure, then you know it doesn't exist, otherwise, if it completes and/or takes longer than a given threshold to return, you can guess that it exists. It's not always perfect, but generally 'filenotfound' requests are quick.

var threshold   = 500,
    successFunc = function(){ console.log('It exists!'); };

var myXHR = $.ajax({
  url: $('#checkme').attr('href'),
  type: 'text',
  method: 'get',
  error: function() {
    console.log('file does not exist');
  },
  success: successFunc
});

setTimeout(function(){
  myXHR.abort();
  successFunc();
}, threshold);

Answer 4

Like Sebastian says it is not possible due to the same origin policy. If the site can be published (temporarily) on a public domain you could use one of the link checker services out there. I am behind checkerr.org

Answer 5

You can $.ajax to it. If file does not exist you will get 404 error and then you can do whatever you need (UI-wise) in the error callback. It's up to you how to trigger the request (timer?) Of course if you also have ability to do some server-side coding you can do a single AJAX request - scan the directory and then return results as say JSON.

Answer 6

As others have mentioned, because of JavaScript's same origin policy, simply using the function from the accepted answer does not work. A workaround to this is to use a proxy server. You don't have to use your own proxy for this, you can use this service for example: https://cors-escape.herokuapp.com (code here).

The code looks like this:

var proxyUrl = "https://cors-anywhere.herokuapp.com/";

function urlExists(url, callback) {
  var sameOriginURL = proxyUrl + url;
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
      callback(xhr.status < 400);
    }
  };
  xhr.open('HEAD', sameOriginURL);
  xhr.send();
}

urlExists(someUrl, function(exists) {
  console.log('"%s" exists?', someUrl, exists);
});