如何使用javascript编写动态文本

I am trying to accomplish something like this :

<?php $url = 'http://www.mydomain.com/img/picture.jpg'; ?>
<img src='<?php echo $url ?>' />

Only the problem is I want to accomplish this using javascript. Something like this

<script>url = 'http://www.mydomain.com/img/picture.jpg'</script>
<img src='<script>document.write(url)</script>' />

Of course it wouldn't work, but you got the idea. Any thought ?

Try - http://jsfiddle.net/m2Prh/

<img id="image" />​

<script>    
    var url = 'http://lorempixel.com/300/200';
    document.getElementById("image").src = url;​
</script>

I suggest reading jquery ,you can acesss every html element