<meta name="viewport" content="width=320" id="mobile">

<meta name="viewport" content="width=1024">

var viewPort = document.createElement('meta');
viewPort.name = "viewport";
viewPort.content = "width=1024";
document.getElementsByTagName('head')[0].appendChild(viewPort);

document.querySelector("meta[name=viewport]")
    .setAttribute("content", "width=1024");