How to go back with saving form data on koa?

Question

JavaScript

There is a router

projectRouter.post("/add",  async ctx => {
    try {
        await Projects.add(ctx.request.body,ctx.state.user.id);
        ctx.redirect('/user/projects/');
    } catch (e) {
        ctx.redirect('back');
    }
});

On error, it returns back to the page with the form, the form data is deleted, but if you press the back button in the browser (next to the url input line), then we go back and the form data is saved.
Or is it impossible to implement such a return on the backend side, without saving the data and substituting it into the template?