Sam Roberts presents Node.js API pitfalls at the Summer 2016 Toronto Node.js meetup.

1. Disclaimer ;-)
Doesn't necessarily reflect the views of IBM, or any of
my Node.js collaborators...
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2. nextTick
• [ ] in next tick of the event loop
• [ ] immediately after A returns
2
process.nextTick(function() {
// Called ...
});

3. nextTick
• [ ] in next tick of the event loop
• [x] immediately after A returns
3
process.nextTick(function() {
// Called ...
});

4. setImmediate
• [ ] in next tick of the event loop
• [ ] immediately after A returns
4
setImmediate(function() {
// Called ...
});

5. setImmediate
• [x] in next tick of the event loop
• [ ] immediately after A returns
5
setImmediate(function() {
// Called ...
});

6. nextTick vs setImmediate
• nextTick: adds callback to queue to be called immediately
• setImmediate: adds callback to queue to be called next tick
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7. worker.kill()
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var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('online', function() {
this.kill('SIGHUP');
})
.on('exit', function() {
console.log('Exit');
});
} else {
process.on('SIGHUP', function() {
console.log('Hup');
});
}

8. worker.kill()
• [ ] "Hup"
• [ ] "Exit"
• [ ] "Hup" and "Exit"
• [ ] No output
8
var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('online', function() {
this.kill('SIGHUP');
})
.on('exit', function() { console.log('Exit'); });
} else {
process.on('SIGHUP', function() { console.log('Hup'); });
}

9. worker.kill()
• [ ] "Hup"
• [x] "Exit"
• [ ] "Hup" and "Exit"
• [ ] No output
9
var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('online', function() {
this.kill('SIGHUP');
})
.on('exit', function() { console.log('Exit'); });
} else {
process.on('SIGHUP', function() { console.log('Hup'); });
}

10. worker.kill() - what is it really?
• Use worker.process.kill() if you want to signal the worker
• Asymetric with worker.send(), worker.on('message', ...), etc.
10
Worker.prototype.kill = function(signo) {
var proc = this.process;
this.once('disconnect', function() {
this.process.kill(signo || 'SIGTERM');
});
this.disconnect();
};

11. worker.suicide - kill the worker
• [ ] true
• [ ] false
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var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('online', function() {
this.kill('SIGTERM');
})
.on('exit', function() {
// this.suicide is ....
});
} else {
}

12. worker.suicide - kill the worker
• [x] true
• [ ] false
12
var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('online', function() {
this.kill('SIGTERM');
})
.on('exit', function() {
// this.suicide is ....
});
} else {
}

13. worker.suicide - exit the worker
• [ ] true
• [ ] false
13
var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('exit', function() {
// this.suicide is ....
});
} else {
process.exit(0);
}

14. worker.suicide - exit the worker
• [ ] true
• [x] false
14
var cluster = require('cluster');
if (cluster.isMaster) {
cluster.fork()
.on('exit', function() {
// this.suicide is ....
});
} else {
process.exit(0);
}

15. worker.suicide - what does it mean?
• worker.disconnect() in parent (implicitly done by worker.kill())
• process.disconnect() in worker
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Actual meaning: "orderly exit"

16. url.parse/format
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var url = require('url');
var uri = url.parse('http://example.com:8080/path');
uri.host = 'ibm.com';
console.log(url.format(uri));
• [ ] yes
• [ ] no
Prints http://ibm.com:8080/path ...

17. url.parse/format
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var url = require('url');
var uri = url.parse('http://example.com:8080/path');
uri.host = 'ibm.com';
console.log(url.format(uri));
• [ ] yes
• [x] no: http://ibm.com/path
Prints http://ibm.com:8080/path ...

18. url.parse/format
• host is "example.com:8080"
• hostname is "example.com"
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19. url.parse/format
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var url = require('url');
var uri = url.parse('http://example.com:8080/path');
uri.hostname = 'ibm.com';
console.log(url.format(uri));
• [ ] yes
• [ ] no
Prints http://ibm.com:8080/path ...

20. url.parse/format
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var url = require('url');
var uri = url.parse('http://example.com:8080/path');
uri.hostname = 'ibm.com';
console.log(url.format(uri));
• [ ] yes
• [x] no: http://example.com:8080/path
Prints http://ibm.com:8080/path ...

21. url.parse/format
• hostname and port are ignored if host is present...
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22. url.parse/format
22
var url = require('url');
var uri = url.parse('http://example.com:8080/path');
delete uri.host;
uri.hostname = 'ibm.com';
console.log(url.format(uri));
• http://ibm.com:8080/path, finally!

23. url.parse/format
• parse: "http://example:8080":
– port is 8080
– host is "example:8080"... why not hostport?
– hostname is "example"... why not host?
• format: hostname and port are ignored if hostname is present
– shouldn't they be prefered if present?
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24. path.parse/format
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var path = require('path');
var bits = path.parse('some/dir/index.txt');
// has: .name, .ext
bits.ext = '.html';
console.log(path.format(bits));
Logs some/dir/index.html...
• [ ] yes
• [ ] no

25. path.parse/format
25
var path = require('path');
var bits = path.parse('some/dir/index.txt');
bits.ext = '.html';
console.log(path.format(bits));
Logs some/dir/index.html...
• [ ] yes
• [x] no: some/dir/index.txt

26. path.parse/format
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var path = require('path');
var bits = path.parse('some/dir/index.txt');
console.log(bits.base); // > index.txt
delete bits.base
bits.ext = '.html';
console.log(path.format(bits));
Logs some/dir/index.html...
• [ ] yes
• [ ] no
Its probably like url...

27. path.parse/format
27
var path = require('path');
var bits = path.parse('some/dir/index.txt');
console.log(bits.base); // > index.txt
delete bits.base
bits.ext = '.html';
console.log(path.format(bits));
Logs some/dir/index.html...
• [ ] yes
• [x] no: some/dir/

28. path.parse/format
28
var path = require('path');
var bits = path.parse('some/dir/index.txt');
bits.base = bits.name + '.html';
console.log(path.format(bits)); // > some/dir/index.html
Its just completely different, format always ignores name and ext.
Correct:

29. streams v1, 2, 3
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Note that, for backwards compatibility reasons, removing 'data' event
handlers will not automatically pause the stream. Also, if there are
piped destinations, then calling pause() will not guarantee that the
stream will remain paused once those destinations drain and ask for
more data.
From https://nodejs.org/api/stream.html#stream_class_stream_readable:

30. streams v1, 2, 3
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Note that, for backwards compatibility reasons, removing 'data' event
handlers will not automatically pause the stream. Also, if there are
piped destinations, then calling pause() will not guarantee that the
stream will remain paused once those destinations drain and ask for
more data.
From https://nodejs.org/api/stream.html#stream_class_stream_readable:
When can we delete backwards compat to v0.8?

31. Question
• Laurie Voss (@seldo), NPM, Nov. 28, 2015
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What kind of node do you want: a good one?
or a (mostly) v0.8 compatible one?
@octetcloud As of right now, 30.4% of registered npm
accounts are less than 6 months old.

32. Answer
• github, twitter, etc..
• Be tolerant (or intolerant) of breakages, but what
you say will effect what happens.
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Its yours (and a lot of other people's) Node.js, speak out:

33. Flames to:
• github: @sam-github
• email: rsam@ca.ibm.com
• twitter: @octetcloud
• talk source: https://gist.github.com/sam-github/4c5c019b92cf95fb6571, or
https://goo.gl/2RWpqE
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