js同比例缩放图片

function DrawImage(ImgD, FitWidth, FitHeight) {
    var image = new Image();
    image.src = ImgD.src;
    if (image.width > 0 && image.height > 0) {
        if (image.width / image.height >= FitWidth / FitHeight) {
            if (image.width > FitWidth) {
                ImgD.width = FitWidth;
                ImgD.height = (image.height * FitWidth) / image.width;
            } else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
        } else {
            if (image.height > FitHeight) {
                ImgD.height = FitHeight;
                ImgD.width = (image.width * FitHeight) / image.height;
            } else {
                ImgD.width = image.width;
                ImgD.height = image.height;
            }
        }
    }
}