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var emSizeDiv;function installEMsize() {
var body = document.body;
var div = document.createElement( "DIV");div.style.position = "absolute";
div.style.top = "10px";
div.style.right = "10px";
div.style.display = "none";div.style.margin = 0;
div.style.padding = 0;
div.style.borderWidth = 0;div.style.lineHeight = "1em";
div.setAttribute( "id", "emsizedetect");
div.appendChild( document.createTextNode( "M"));body.appendChild( div);
emSizeDiv = document.getElementById( "emsizedetect");
}function getEMsize() {
var emSize;if(!emSizeDiv) installEMsize();
emSizeDiv.style.display = "block";
emSize = emSizeDiv.offsetHeight;
emSizeDiv.style.display = "none";return emSize;
}
This will detect the document's default font-size in pixels. No matter if it's not defined, or defined in something other than pixels, pt or % for example.
It works in IE6, IE7 and FF.
It's also sensitive to browser font size changes, I know in IE at least this doesn't change the font size applied to <body>.
Just call getEMsize() as many times as you like. No need to run the install function yourself, it'll do this automatically.
