How to insert metatag without using jquery append?

I used the following jquery to insert a metatag into a html document.

<script type="text/javascript">
if(screen.width>=320 && screen.width<=767){
$('head').append('<meta id="viewport" name="viewport" content="width=320; initial-scale=1.0; maximum-scale=1.0; user-scalable=0;">');}    
</script>

If possible, I'd like to insert the metatag without using jquery. Anyone have any ideas how I can do that?

I believe I will probably need to use document.getElementByTagName but I'm not sure how.

Just in case you are wondering, I am inserting the metatag into my html to to optomize the site for viewing with the ipho开发者_运维技巧ne. Unfortunately, width=device-width is not an option as it doesn't play well with my ipad version.

var viewPortTag=document.createElement('meta');
viewPortTag.id="viewport";
viewPortTag.name = "viewport";
viewPortTag.content = "width=320, initial-scale=1.0, maximum-scale=1.0, user-scalable=0";
document.getElementsByTagName('head')[0].appendChild(viewPortTag);

Javascript solution:

document.getElementsByTagName('head')[0].innerHTML += '<meta id="viewport" name="viewport" content="width=320; initial-scale=1.0; maximum-scale=1.0; user-scalable=0;">';

You can also use "setAttribute" (rather than the "dot" notation) for weirdo attribute names (that contain non-alpha-numeric characters).

Example:

var iefix=document.createElement('meta');
iefix.setAttribute("http-equiv", "X-UA-Compatible");
iefix.setAttribute("content", "IE=Edge");
document.getElementsByTagName('head')[0].appendChild(iefix);

The example above causes IE (<=9) to always use the latest document standards mode. Sometimes IE will fall back to older standards, and therefore break your modern javascript / canvas web app.

Here is a solution that creates a meta tag, if it does not already exist:

var viewport = document.querySelector('meta[name=viewport]');
var viewportContent = 'width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=0';

if (viewport === null) {
  var head = document.getElementsByTagName('head')[0];
  viewport = document.createElement('meta');
  viewport.setAttribute('name', 'viewport');
  head.appendChild(viewport);
}

viewport.setAttribute('content', viewportContent);