using javascript to detect whether the url exists before display in iframe

Question

I'm using javascript to pass a dynamic url to iframe src. but sometimes the url does not exist, how could i detect the non-exist url beforehand, so that i can hide the iframe that with 404 error.

Answer 1

Due to my low reputation I couldn't comment on Derek 朕會功夫's answer. I've tried that code as it is and it didn't work well. There are three issues on Derek 朕會功夫's code.

1. The first is that the time to async send the request and change its property 'status' is slower than to execute the next expression - if(request.status === "404"). So the request.status will eventually, due to internet band, remain on status 0 (zero), and it won't achieve the code right below if. To fix that is easy: change 'true' to 'false' on method open of the ajax request. This will cause a brief (or not so) block on your code (due to synchronous call), but will change the status of the request before reaching the test on if.

2. The second is that the status is an integer. Using '===' javascript comparison operator you're trying to compare if the left side object is identical to one on the right side. To make this work there are two ways:

   • Remove the quotes that surrounds 404, making it an integer;
   • Use the javascript's operator '==' so you will be testing if the two objects are similar.

3. The third is that the object XMLHttpRequest only works on newer browsers (Firefox, Chrome and IE7+). If you want that snippet to work on all browsers you have to do in the way W3Schools suggests: w3schools ajax

The code that really worked for me was:

var request;
if(window.XMLHttpRequest)
    request = new XMLHttpRequest();
else
    request = new ActiveXObject("Microsoft.XMLHTTP");
request.open('GET', 'http://www.mozilla.org', false);
request.send(); // there will be a 'pause' here until the response to come.
// the object request will be actually modified
if (request.status === 404) {
    alert("The page you are trying to reach is not available.");
}