Express: run app.render asynchronously

[AbdelrahmanHafez]

Is there a way to run app.render asynchronously?

I tried promisifying it using bluebird but I get an error

    let render = Promise.promisify(req.app.render);
    html = await render('email', { email: '[email protected]' });

output:

TypeError: Cannot read property 'cache' of undefined

[fredski02]

https://github.com/expressjs/express/blob/3ed5090ca91f6a387e66370d57ead94d886275e1/lib/response.js#L973-L981 - I think the problem is that render is trying to send back the response. So even if you did manage to delay the render method and do it later on, you'd get an error saying headers already sent. However, if you read the comments of the render function in the link i provided, you can pass a callback to stop the response being done automatically. I hope this helps. Try passing a false boolean to the cache as well

[AbdelrahmanHafez]

Okay, that link points to res.render instead of app.render, but it pointed my into the right direction.
When I made render into it's own variable, it lost the reference to this, so in order to fix it, you would

    const Promise = require('bluebird');

    req.app.renderAsync = Promise.promisify(req.app.render);
    let html = await req.app.renderAsync('email', { email: '[email protected]' });

That actually works, thanks @fredski02