Get the content type for a certain URL.

getContentType.js

function getContentType(url,callback){
	var oReq = new XMLHttpRequest();
	oReq.onreadystatechange = function(){
		if(this.readyState == this.DONE){
			callback(this.getResponseHeader("content-type"));
		}
	};
	oReq.open("head", url, true);
	oReq.send();
}