const Koa = require('koa');
const app = new Koa();
const jsonp = require('koa-response-jsonp');

jsonp(app);

app.use(async ctx => {
	ctx.jsonp({
		success: true
	});
});

app.listen(3000);

fn({"success":true})

jsonp(app, {
	callbackFn: 'cb'
});