Question

How does this code sample differ from a normal function declaration paired with an if statement for the event trigger? Is brevity the only advantage?

xmlhttp.onreadystatechange=function()
{
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
  }

Answer 1

In Javascript you may have what is called an anonymous function. In the above code, the anonymous function will be executed when the xmlhttp.onreadystatechange event is fired. Other examples are:

window.onkeypress = function(e) {
    alert(String.fromCharCode(e.which));
}

Or you could create an anonymous variable-function…

var myFunc = function(msg) {    // Create function and assign to var
    alert(msg);
}
myFunc("Hello World");          // Call new 'function'