Question

<div id="myDiv"></div>
<script>                    
    var xmlhttp = new XMLHttpRequest();
    document.getElementById("myDiv").innerHTML += xmlhttp.readyState + "<br/>";
    xmlhttp.onreadystatechange = function() {
        document.getElementById("myDiv").innerHTML += xmlhttp.readyState + "<br/>";
    }
    xmlhttp.open("GET", "example.com", true);
    xmlhttp.send();
</script>

I get this in display:

0
1
1
2
3
4

Why there are two 1s?

My browser is firefox 17.0.

Answer 1

Ready states are well defined for XML HTTP object: https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#Properties.

But sequences of ready states seem to be different for every browser, so you can’t rely on particular sequence of states in your code.

FF 19: 0, 1, 1, 2, 3, 4

Chrome 24: 0, 1, 2, 3, 4

Opera 12.12: 0, 1, 2, 3, 4

Safari 5.1: 0, 1, 2, 3, 4

IE 9: 0, 1, 1, 2, 3, 4

You can test your browser here.