Detect presense of dial-up internet connection in Javascript/DHTML/HTML

Posted on 2004-10-09
Medium Priority
Last Modified: 2010-04-06
I'm trying to revamp my local homepage to incorporate an automatic option that detects the presence of an internet connection. In the case of an internet connection, the browser redirects to an internet website [in this case, gmail.com], and otherwise, it loads a page local to my computer.

Though i'm farirly javascript and html literate [assuming this is possible], a semi-lamen's termed walkthrough would be greatly appreciated. I really hope this is possible. Thanks.
Question by:jonnylentilbean
  • 2

Accepted Solution

techjosh earned 500 total points
ID: 12426454
So, heres how it works... you set the imgsrc variable to an image that is always available when you are online.
You set the online_url to the url you want to go to if you are online and the offline_url to the url you want to go to if you're offline.

The javascript Image() object tries to download the image at imgsrc... if it can it runs the onload function... if it cant it runs the onerror function... if you cancel the page load it runs the onabort function... onabort and onerror both execute the offline function while onload executes the online function... hope its not too cryptic.

Also, if your browser caches the image it may report itself being online when you are really offline.

<title>Online test</title>
<script language=javascript>
var imgsrc = "http://www.google.com/images/logo_sm.gif";
var online_url = "http://www.google.com";
var offline_url = "c:\\offline.htm";

function TestConnection()
      var img = new Image();
      img.onabort = Offline;
      img.onerror = Offline;
      img.onload = Online;

      img.src = imgsrc;

function Online()
      alert ("You are online!");
      document.location.href = online_url;

function Offline()
      alert ("You are offline!");
      document.location.href = offline_url;

<body onload="TestConnection();">
<H1>Please Wait...</H1>

Expert Comment

ID: 12427755
If you have a problem with your browser caching the image so that the page always says it's online you need to find an image that isn't cached... lots of dynamic images are like this.

try this image if you have this problem:
var imgsrc = "http://www.danasoft.com/vipersig.jpg";

If that fixes your problem you probably want to find another dynamic image as it might be considered rude to use his image and his bandwidth to see if you are online.

Featured Post

Train for your Pen Testing Engineer Certification

Enroll today in this bundle of courses to gain experience in the logistics of pen testing, Linux fundamentals, vulnerability assessments, detecting live systems, and more! This series, valued at $3,000, is free for Premium members, Team Accounts, and Qualified Experts.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

There are two main kinds of selectors in CSS: One is base selector like h1, h2, body, table or any existing HTML tags.  For instance, the following rule sets all paragraphs (<p> elements) to red: (CODE) CSS also allows us to define our own custom …
I found this questions asking how to do this in many different forums, so I will describe here how to implement a solution using PHP and AJAX. The logical flow for the problem should be: Write an event handler for the first drop down box to get …
Viewers will learn about if statements in Java and their use The if statement: The condition required to create an if statement: Variations of if statements: An example using if statements:
The viewer will learn how to look for a specific file type in a local or remote server directory using PHP.

621 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question