Achieving min-width with viewport meta tag

So you want to change the viewport tag’s width dynamicaly .

Here you go :

<meta id="myViewport" name="viewport" content="width = 380">
<script>
window.onload = function () {
    var mvp = document.getElementById('myViewport');
    mvp.setAttribute('content','width=580');
}
</script> 

See:http://www.quirksmode.org/mobile/tableViewport.html