Can app.render() render an array of views? - node.js

Question

It does not seem to be documented, I was wondering if it is possible to render multiple views or an array of views in Expressjs like so:
const data = 'some data passed by a DB';
const app = express();
const arrayViews = ['layout','email', 'web'];
app.render(arrayViews, data, (err, html) => {
if (err) throw err;
})
or do I have to do it in multiple instances
app.render('email', data, (err, html) => {
if (err) throw err;
})
app.render('web', data, (err, html) => {
if (err) throw err;
})

Answer 1

No. You cannot pass an array of views to app.render(). The point of app.render() is to create ONE piece of rendered HTML that can be sent as a response to a particular http request. You can't send multiple responses to one http request. So, you only want to call res.render() once for any given request.
If you want to have two different types of responses for different situations, then you should either make a separate route for each response and call res.render() once in each response with the appropriate template for that request.
Or, you can pass in a query parameter in the URL and use an if statement in the route handler to decide which template to render. But, the point is that you send exactly one response for each request.
For example, here's looking at a query parameter to decide which type of render to do:
app.get('/mypage', function(req, res) {
if (req.query.page === "email") {
res.render('email', data);
} else {
res.render('web', data);
}
});
Otherwise, you'd have two separate routes:
app.get('/mypage/email', function(req, res) {
res.render('email', data);
});
app.get('/mypage/web', function(req, res) {
res.render('web', data);
});
I may have originally been confused about the point of your question (since you don't show the overall context of your render or what you're using it for).
If you're using app.render() to collect the HTML from rendering operations, you can call that multiple times and wait for all to be done and then you have multiple rendered templates which you can do whatever you want with. But, a single app.render() doesn't accept multiple templates. You'd have to call it multiple times and wait for all the requests to be done.
Promise.all([appRender('email'), appRender('web')]).then([email, web] => {
// can access both rendered templates here
// to do with them whatever you want to do
}).catch(err => {
// error here
});
Or, you could use this to make a version of app.render() that would take an array:
const util = require('util');
const appRender = util.promisify(app.render.bind(app));
app.renderAll = function(arrayOfTemplates) {
return Promise.all(arrayOfTemplates.map(template => {
return appRender(template);
}));
});
app.renderAll(['email', ['web']]).then([email, web] => {
// can access both rendered templates here
// to do with them whatever you want to do
}).catch(err => {
// error here
});