Author: John Au-Yeung

Sometimes, we want to read a stream into a buffer with Node.js.

In this article, we’ll look at how to read a stream into a buffer with Node.js.

How to read a stream into a buffer with Node.js?

To read a stream into a buffer with Node.js, we can use the on method to listen for the data event.

For instance, we write

const bufs = [];
stdout.on('data', (d) => {
  bufs.push(d);
});
stdout.on('end', () => {
  const buf = Buffer.concat(bufs);
})

to call stdout.on with 'data' to listen for the data event.

In the callback, we call bufs.push with d to append d into the bufs array.

And then we call on with 'end' to listen to the end event which is triggered when the stream is finished.

In the callback, we call Buffer.concat with bufs to combine the buffer chunks into a single buffer object.

Conclusion

To read a stream into a buffer with Node.js, we can use the on method to listen for the data event.

Sometimes, we want to convert a MongoDB object ID to string with Node.js.

In this article, we’ll look at how to convert a MongoDB object ID to string with Node.js.

How to convert a MongoDB object ID to string with Node.js?

To convert a MongoDB object ID to string with Node.js, we can use the object ID toString method.

For instance, we write

user._id.toString()

to convert the _id value to a string.

Conclusion

To convert a MongoDB object ID to string with Node.js, we can use the object ID toString method.

Sometimes, we want to implement user permissions with Node.js and Express.js

in this article, we’ll look at how to implement user permissions with Node.js and Express.js.

How to implement user permissions with Node.js and Express.js?

To implement user permissions with Node.js and Express.js, we can define a function that returns a middleware function that checks the role of the user and acts accordingly.

For instance, we write

const requireRole = (role) => {
  return (req, res, next) => {
    if (req.session.user && req.session.user.role === role) {
      next();
    } else {
      res.send(403);
    }
  }
}

app.get("/foo", foo.index);
app.get("/foo/:id", requireRole("user"), foo.show);
app.post("/foo", requireRole("admin"), foo.create);

app.all("/foo/bar", requireRole("admin"));
app.all("/foo/bar/*", requireRole("user"));

to define the requireRole function that returns a middleware function that checks the role of the user with req.session.user.role === role.

And if the user has the role, then we call next to call the route middleware.

Otherwise, we return a 403 response.

Then we use requireRole by calling it with the role name before the route handler method in app.get, app.post, and app.all.

Conclusion

To implement user permissions with Node.js and Express.js, we can define a function that returns a middleware function that checks the role of the user and acts accordingly.

Sometimes, we want to quit a Node.js app gracefully.

In this article, we’ll look at how to quit a Node.js app gracefully.

How to quit a Node.js app gracefully?

To quit a Node.js app gracefully, we can listen for the SIGINT event and call process.exit when it’s triggered.

For instance, we write

process.on('SIGINT', () => {
  process.exit();
})

to listen to the SIGINT event by calling process.on with 'SIGINT'.

In the event handler callback, we call process.exit without an an exit code to exit the app gracefully.

Conclusion

To quit a Node.js app gracefully, we can listen for the SIGINT event and call process.exit when it’s triggered.

Sometimes, we want to wait until an element is visible with Puppeteer.

In this article, we’ll look at how to wait until an element is visible with Puppeteer.

How to wait until an element is visible with Puppeteer?

To wait until an element is visible with Puppeteer, we call the page.waitForSelector method.

For instance, we write

const puppeteer = require('puppeteer');

const wait = async () => {
  const browser = await puppeteer.launch()
  const page = await browser.newPage();
  await page
    .waitForSelector('#myId')
  console.log('got it')
  browser.close();
}

to call puppeteer.launch to launch Puppeteer.

Then we call browser.newPage to open the page.

And then we call page.waitForSelector with the CSS selector of the element we want to wait for.

Then once we’re done, we call browser.close to close the browser.

Conclusion

To wait until an element is visible with Puppeteer, we call the page.waitForSelector method.