My Programming Tricks

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The viewport parameter in the HTML Meta Tag is used to limit the screen width. Another thing to pay attention for these codes is the neccessity to differentiate between tablets and phones. Phones tend to have less resolution whereas tablets can have resolutions comparable to that of PC or Mac. I use a simple criteria to differentiate the two by checking the screen width whether it is wider than 700 pixels. If so, tablets' width will be forced to limit to only 700 pixels. For non-tablets, the width will be limited to the native screen width found in the Javascript system parameter screen.width. Pay attention to when orientation changes. Android will have the width and height paramters swapped whereas the mobile Safari will have the same width and height irregardless of the orientation.

The <body> onorientationchange is used to listen to the orientation change even. Whenever it is fired, the 'content' meta will be reconfigured according to the orientation status. Javascript's window.orientation is used to check the current orientation status in terms of degrees.

Let's jump into the codes:

<html>
<head>
<title>Javascript to Limit HTML Width for Mobile Devices of Any Orientation</title>

<script>

var mobile = navigator.userAgent.match(/Android/i) || navigator.userAgent.match(/BlackBerry/i) || navigator.userAgent.match(/iPhone|iPad|iPod/i) || navigator.userAgent.match(/Opera Mini/i) || navigator.userAgent.match(/IEMobile/i);

var safari = navigator.userAgent.match(/iPhone|iPad|iPod/i) && navigator.userAgent.match(/Safari/i);

var ot = ""; // variable "orientation" is used by mobile browsers
if (safari) {
if (window.orientation == 0) { ot="portrait"; } else { ot="landscape"; }
}
else {
if (screen.width<screen.height) { ot="portrait"; } else { ot="landscape"; }
}

if (mobile) {
var mobileWidth = getMobileWidth();
alert("setting the width of "+mobileWidth);
document.write('<meta id="vp" name="viewport" content="width = '+mobileWidth+', initial-scale=1.0">');
}
// if it is not mobile, viewport is not supported or will be ignored

function getMobileWidth() {
var width;
var isTablet = 0;
if (safari) { // safari screen width and height remain constant irregradless of the orientation
  if (ot == "portrait") { width = screen.width; if (width>400) {isTablet=1;} }
  else { width = screen.height; if (width>700) {isTablet=1;} }
}
else {
  width = screen.width;
  if (ot == "portrait") { if (width>400) {isTablet=1;} }
  else { if (width>700) { isTablet=1;} }
}
if (isTablet) {
  if (ot == "portrait") {
   return 400;
  }
  else {
   return 700;
  }
}
else {
  return width;
}
}

function changeViewPort() { //change viewport dynamically by changing the meta 'content' attribute

if (safari) { // mobile safari will not swap screen.width with screen.height after orientation change
  if (window.orientation == 0) { ot="portrait"; } else { ot="landscape"; }
}
else { // other broswers will have height and width swapped
  if (screen.width<screen.height) { ot="portrait"; } else { ot="landscape"; }
}

var mobileWidth = getMobileWidth();
alert("setting the width of "+mobileWidth);
alert("screen in "+ot+" mode w:"+screen.width+" h:"+screen.height+" -->"+window.orientation);

if (mobile) {
  var vp = document.getElementById('vp');
  vp.setAttribute('content','width='+mobileWidth+', initial-scale=1.0');
}
}

</script>

</head>

<body bgcolor=orange onorientationchange="changeViewPort()">

<table width=100% height=100% align=center valign=middle>
<tr><td width=100% height=100% align=center valign=middle style="font-family: Lucida Sans, Lucida Sans Unicode, Helvetica, Arial, sans-serif;">Under Construction</td></tr>
</table>

</body>

</html>

Please note the meta tag has been given an ID (id="vp") so that it can be modified when necessary. onorientationchange is used instead of "onresize" as "onresize" will make give a lots of false signal even when the address bar in mobile browsers shows up or hides.

My Programming Tricks

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Monday, August 28, 2017

Javascript to Limit HTML Width for Mobile Devices of Any Orientation