How to calculate approximately the connection speed of a website using JavaScript?

Question

How to calculate approximately the connection speed of a website using JavaScript?

I want to create a javascript widget like, which will calculate the speed opening the current opened page.

I am asking if this can be done using just javascript and what will be the idea.

Update

Note that the page size is always Unknown.

Answer 1

Sure.

<script>
    startTime = Date.now();
    window.onload = function(){
        endTime = Date.now();
        //Time in ms between opening page, and loading all the date
        alert(endTime - startTime)
    };
</script>

Now to approximate speed. Statically you know let's say page is 200kb.

var kbps = 200 / (endTime - startTime * 1000);

Answer 2

Here's an example using AJAX with .Net backend, though it could be anything.

Here's a simpler example using an image.

The key is to have a page/object of a known size and capture the start and end times as the browser retrieves it. Then simply divide the size by some [unit of time] to get [size] per [unit of time]. Then use math to translate this into whatever you want.