Creating a promise for rendering templates in NodeJS

Question

i am trying to create a function for rendering views in NodeJS that will be called using await later on.

const getTemplate = async (template, context) => {
  app.render(template, { data: context }, (error, html) => {
    return html;
  });
}

const data = require('./data.json');

app.get('/pdf', async (req, res) => {
  const html = await getTemplate('invoice', data);
  res.send(html);
});

Right now it gives me an empty response and that's probably because it exits the getTemplate function before the render callback fires, but i don't know how to modify it in an elegant way.

You never return anything from getTemplate. You must promisify app.render or build a promise yourself. — Denys Séguret, Jan 02 '19 at 15:22

score 3 · Accepted Answer · answered Jan 02 '19 at 15:26

You need to return a promise from getTemplate. Since you want to wait for the app.render to finish, I hope the following code does what you intend to do :)

// `async` is not really necessary as you are not using `await`, but you may provide it, if you want
const getTemplate = /* async */ (template, context) => {
  return new Promise((resolve, reject) => {
    app.render(template, { data: context }, (error, html) => {
      if (error) return reject(error);
      return resolve(html);
    });
  });
}

const data = require('./data.json');

app.get('/pdf', async (req, res) => {
  const html = await getTemplate('invoice', data);
  res.send(html);
});

Not that it's wrong but I tend to prefer `if (error) reject(error); else resolve(html);` to emphasize that the callback doesn't really use a `return` value, since it's ignored. — Patrick Roberts, Jan 02 '19 at 15:56

Creating a promise for rendering templates in NodeJS

1 Answers1