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JavaScript Node.js Basics (2014) Building a Command Line Application Handling Errors in Node

Daniel Granger
PLUS
Daniel Granger
Courses Plus Student 19,857 Points
Posted by Daniel Granger
Daniel Granger
Courses Plus Student 19,857 Points

.on("error", function(){...}); Not catching Error event.

My code is not catching the error event, instead it just shows:

_http_client.js:25
      throw new Error('Unable to determine the domain name');
      ^

Error: Unable to determine the domain name
    at new ClientRequest (_http_client.js:25:13)
    at Object.exports.request (http.js:31:10)
    at Object.exports.get (http.js:35:21)
    at Object.<anonymous> (/Users/d/Sites/sandbox/JavaScript/Node/treehouseApp.js:13:20)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Function.Module.runMain (module.js:447:10)
    at startup (node.js:140:18)

Here is my code:

// Connect to the API URL (http://teamtreehouse/username.json)
var request = http.get("teamtreehouse.com/" + username + ".json", function(response){
  console.log(response.statusCode);
  // Read the data
  // Parse the data
  // Print the data
});

request.on("error", function(e){
  console.error(e.message);
});

As per the instructions in the video, the protocol in the URL has been omitted to ensure an error is thrown, however the error event is not caught and thus console.error(e.message); is not shown.

I'm using Node.js 5.6.0.

Thanks

4 Answers

Chad Donohue
Chad Donohue
5,657 Points

There is an error being thrown in the request method, so this behavior will now be different than that posted in the video. The change was made here

This changed was introduced in Node 5.0.0 here

The workspace version of Node is 4.2.6

Chris Skinner
Chris Skinner
3,807 Points
Chris Skinner
Chris Skinner
3,807 Points

So what does this mean in terms of forcing / caching an error for demonstration purposes - is there a work around / solution\?

Dom Farnham
Dom Farnham
19,421 Points
Dom Farnham
Dom Farnham
19,421 Points

Good to know. Thanks

Manav Misra
Manav Misra
11,778 Points

More specifically, using this worked:

var request = https.get({host:"teamtreehouse.com/" + username + ".json"}, function(response){

http://stackoverflow.com/questions/32675907/how-to-deal-with-unhandled-error-event-error-nodejs

Kirill Babkin
Kirill Babkin
19,940 Points
Kirill Babkin
Kirill Babkin
19,940 Points

i did this.

var https = require("https")

// print message
try{
var request = https.get("teamtreehouse.com/username.json",function(response){
  console.log(response.statusCode);  // print the data
});

} catch(e) {

      console.error(e.message);
}
Kirill Babkin
Kirill Babkin
19,940 Points
Kirill Babkin
Kirill Babkin
19,940 Points

try{ }catch(error){ } block works on all errors. request.on("error", function(e){ console.error(e.message); }); may not work depending on the version of node.

Anthony Albertorio
Anthony Albertorio
22,624 Points

Great suggestion. Works like a charm. This video needs updating to avoid confusion. Thanks!

Sebastian Röder
Sebastian Röder
13,878 Points
Sebastian Röder
Sebastian Röder
13,878 Points

A better way to simulate the error event is keep the correct URL intact:

"http://teamtreehouse.com/" + username + ".json"

and instead disconnect your internet connection temporarily while you execute node app.js. This will result in the following error event:

$ node app.js 
events.js:154
      throw er; // Unhandled 'error' event
      ^

Error: getaddrinfo ENOTFOUND teamtreehouse.com teamtreehouse.com:443
    at errnoException (dns.js:26:10)
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:77:26)

If you handle the error event in the callback, as described in the video, the error message will look like this instead:

$ node app.js 
getaddrinfo ENOTFOUND teamtreehouse.com teamtreehouse.com:443
Brendan Moran
Brendan Moran
14,052 Points
Brendan Moran
Brendan Moran
14,052 Points

The documentation is a bit confusing, too. I tried exactly what it says in the documentation for an HTTPS request error:

const https = require('https');

https.get('https://encrypted.google.com/', (res) => {
  console.log('statusCode: ', res.statusCode);
  console.log('headers: ', res.headers);

  res.on('data', (d) => {
    process.stdout.write(d);
  });

}).on('error', (e) => {
  console.error(e);
});

Notice that the error handler is on the response, not the request. I found this confusing, because in the HTTP documentation, it is on the request, like this:

http.get('http://www.google.com/index.html', (res) => {
  console.log(`Got response: ${res.statusCode}`);
  // consume response body
  res.resume();
}).on('error', (e) => {
  console.log(`Got error: ${e.message}`);
});

I tried both, and Andrew's way. None of it worked, so that leaves me confused as to why the currently documented way does't work, either. "node- v" command is showing 6.2.2 for me in the workspaces console. The try/catch method did work, though, so thank you Kirill Babkin for that.