As with any kind of app, there are difficult issues to solve when we write Node apps. In this article, we’ll look at some solutions to common problems that we might encounter when writing Node apps.

Log Inside page.evaluate with Puppeteer

We can log output when page.evaluate is run by listening to the consoleevent.

For instance, we can write:

const page = await browser.newPage();
page.on('console', consoleObj => console.log(consoleObj.text()));

We call browser.newPage to create a new page object.

Then we listen to the console event with it.

It takes a callback, which we can convert to text with the text method.

Testing Asynchronous Function with Mocha

We can run async functions with Mocha tests to test them.

For instance, we can write:

it('should do something', async function() {
  this.timeout(40000);
  const result = await someFunction();
  assert.isBelow(result, 3);
});

We call this.timeout to set the timeout before the test times out.

Then we use await to run our async function, which returns a promise.

Finally, we get the result and use assert to check it.

Acknowledgment for socket.io Custom Event

We can listen to events after a connection is established.

On the server-side, we can listen to the connection event to see if a connection is established.

Once it is, then we emit an event to acknowledge the connection is made.

Likewise, we can do the same on the client-side.

For instance, in our server-side code, we write:

io.sockets.on('connection', (sock) => {
   sock.emit('connected', {
     connected: 'yes'
   });
   sock.on('message', (data, callback) => {
     console.log('received', data);
     const responseData = {
       hello: 'world'
     };

     callback(responseData);
   });
 });

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