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;
}
}
}
}