javascript - Why does is my onchange event triggered when my page loads instead of when I click my radio button? -

i have following code in javascript. i'd alert happen wnen user checks radio button, instead happens when page loads, , nothing happens when radio button gets checked. why?

var myradiobutton = document.getelementbyid("myradiobutton"); myradiobutton.onchange=alert("checked!"); 

the radio button starts off unchecked. in html looks this:

<div class="myradiobutton"><input type="radio" id="myradiobutton" name="radiobuttons"  />&nbsp; radio button  </div> 

why on earth javascript think onchange event has occurred when page loads? , why doesn't recognize change when check radio button?

in fact, whatever element use "onchange" makes alert pop when page loads, without user interaction @ all. misunderstanding how "onchange" works?

what mean is

myradiobutton.onchange = function() { alert('checked'); }; 

what did execute alert-function , assign return value of function event handler onchange event (which nothing when executed)