见代码（html）
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<!--<meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=2.0,user-scalable=1"/>-->
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body onload= "bodyfinish()">
<div id="unit" style=" 320px; height:48px; position:relative;">
<p>mogoads</p>
</div>
</body>
<script type="text/javascript">
function bodyfinish(){
var include = false;
var metas = document.getElementsByTagName('meta');
var i;
console.log("for begin");
for (i=0; i<metas.length; i++) {
if (metas[i].name == "viewport") {
include = true;
metas[i].content = "width=device-width, minimum-scale=1.0, maximum-scale=2.0, user-scalable=1";
console.log("in for set meta");
break;
}
}
if(!include){
console.log("set meta");
var head = document.getElementsByTagName('head')[0];
console.log("set meta after %s",head);
var newElement = document.createElement('meta');
newElement.setAttribute('name', 'viewport');
newElement.setAttribute('content', 'width=device-width,initial-scale=1.0,minimum-scale=1.0,maximum-scale=2.0,user-scalable=1');
head.appendChild(newElement);
var s = document.getElementsByTagName('meta');
for(i=0;i<s.length; i++){
console.log("%d",i);
if (s[i].name == "viewport") {
var content_s = s[i].content;
console.log("viewport have add");
}
}
}
}
</script>
</html>
重点是这个javascript
var newElement = document.createElement('meta');
newElement.setAttribute('name', 'viewport');
newElement.setAttribute('content', 'width=device-width,initial-scale=1.0,minimum-scale=1.0,maximum-scale=2.0,user-scalable=1');
head.appendChild(newElement);
关于meta 中参数的使用请参看
http://blog.caesarchi.com/2012/05/html-viewport-meta.html
http://www.w3.org/TR/css-device-adapt/#the-lsquomax-zoomrsquo-property