rotating a div line to follow mouse

calculate an angle for a div rotation based on mouse coordinates

by TheBanana

HTML

<div id="line">
    <div>

CSS

#line {
    position:absolute;
    left:200px;
    top:200px;
    width:200px;
    height:5px;
    background:green;
    transform-origin: 0% 0%;
    transform:rotate(45deg);
}

JavaScript

$(function () {
    $(document).on("mousemove", function (ev) {
        var x1 = 200,
            y1 = 200;
        var x2 = ev.clientX,
            y2 = ev.clientY;
        var d =  Math.sqrt(Math.pow((y2 - y1),2)+Math.pow((x2 - x1),2));
        var angle = Math.round(Math.atan2((y2 - y1) , (x2 - x1)) * (180 / (4 * Math.atan(1))));
        console.log(angle);
        $("#line").css({
            "transform":"rotate("+angle+"deg)",
            "width":d+"px"
        });
    });
});