Obscure element by ID automatically on a webpage

text_obscurer.js

//just a little alternative to the eye-ball-icon revealer that is meant for sensitive information on a page (to mitigate shoulder-surfing attacks).
(function() {
    document.onmousemove = handleMouseMove;
    function handleMouseMove(event) {
        var eventDoc, doc, body;

        event = event || window.event; // IE-ism

        // If pageX/Y aren't available and clientX/Y are,
        // calculate pageX/Y - logic taken from jQuery.
        // (This is to support old IE)
        if (event.pageX == null && event.clientX != null) {
            eventDoc = (event.target && event.target.ownerDocument) || document;
            doc = eventDoc.documentElement;
            body = eventDoc.body;

            event.pageX = event.clientX +
              (doc && doc.scrollLeft || body && body.scrollLeft || 0) -
              (doc && doc.clientLeft || body && body.clientLeft || 0);
            event.pageY = event.clientY +
              (doc && doc.scrollTop  || body && body.scrollTop  || 0) -
              (doc && doc.clientTop  || body && body.clientTop  || 0 );
        }

        // Use event.pageX / event.pageY here
		var sensitiveElement = document.getElementById("REPLACEME_PLAINTEXT_TEXT_BOX_ID");
		var targetLoc = sensitiveElement.getBoundingClientRect();
		var fudgeFactor = .025;
		console.log(targetLoc.top +"-"+ event.pageY+"  +  "+targetLoc.right +"-"+ event.pageX);

		var targetWidth =  targetLoc.right - targetLoc.left;
		var targetHeight = targetLoc.bottom - targetLoc.top;
		console.log("width,height"+targetWidth+","+targetHeight);
		blurFactor = Math.sqrt(fudgeFactor*Math.pow(targetLoc.bottom - targetHeight/2 - event.pageY,2) + fudgeFactor*Math.pow(targetLoc.left + targetWidth/2 - event.pageX,2)) / 101;
		blurFactor = Math.min(Math.round(blurFactor * 1000) / 1000, .45);
		console.log(blurFactor);
		$(sensitiveElement).css("filter","blur("+ blurFactor + "rem)");
    }
})();