1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
|
# process
<!-- type=global -->
The `process` object is a global object and can be accessed from anywhere.
It is an instance of [EventEmitter][].
## Event: 'exit'
Emitted when the process is about to exit. This is a good hook to perform
constant time checks of the module's state (like for unit tests). The main
event loop will no longer be run after the 'exit' callback finishes, so
timers may not be scheduled.
Example of listening for `exit`:
process.on('exit', function() {
setTimeout(function() {
console.log('This will not run');
}, 0);
console.log('About to exit.');
});
## Event: 'uncaughtException'
Emitted when an exception bubbles all the way back to the event loop. If a
listener is added for this exception, the default action (which is to print
a stack trace and exit) will not occur.
Example of listening for `uncaughtException`:
process.on('uncaughtException', function(err) {
console.log('Caught exception: ' + err);
});
setTimeout(function() {
console.log('This will still run.');
}, 500);
// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');
Note that `uncaughtException` is a very crude mechanism for exception
handling and may be removed in the future.
Don't use it, use [domains](domain.html) instead. If you do use it, restart
your application after every unhandled exception!
Do *not* use it as the node.js equivalent of `On Error Resume Next`. An
unhandled exception means your application - and by extension node.js itself -
is in an undefined state. Blindly resuming means *anything* could happen.
Think of resuming as pulling the power cord when you are upgrading your system.
Nine out of ten times nothing happens - but the 10th time, your system is bust.
You have been warned.
## Signal Events
<!--type=event-->
<!--name=SIGINT, SIGUSR1, etc.-->
Emitted when the processes receives a signal. See sigaction(2) for a list of
standard POSIX signal names such as SIGINT, SIGUSR1, etc.
Example of listening for `SIGINT`:
// Start reading from stdin so we don't exit.
process.stdin.resume();
process.on('SIGINT', function() {
console.log('Got SIGINT. Press Control-D to exit.');
});
An easy way to send the `SIGINT` signal is with `Control-C` in most terminal
programs.
## process.stdout
A `Writable Stream` to `stdout`.
Example: the definition of `console.log`
console.log = function(d) {
process.stdout.write(d + '\n');
};
`process.stderr` and `process.stdout` are unlike other streams in Node in
that writes to them are usually blocking. They are blocking in the case
that they refer to regular files or TTY file descriptors. In the case they
refer to pipes, they are non-blocking like other streams.
## process.stderr
A writable stream to stderr.
`process.stderr` and `process.stdout` are unlike other streams in Node in
that writes to them are usually blocking. They are blocking in the case
that they refer to regular files or TTY file descriptors. In the case they
refer to pipes, they are non-blocking like other streams.
## process.stdin
A `Readable Stream` for stdin. The stdin stream is paused by default, so one
must call `process.stdin.resume()` to read from it.
Example of opening standard input and listening for both events:
process.stdin.resume();
process.stdin.setEncoding('utf8');
process.stdin.on('data', function(chunk) {
process.stdout.write('data: ' + chunk);
});
process.stdin.on('end', function() {
process.stdout.write('end');
});
## process.argv
An array containing the command line arguments. The first element will be
'node', the second element will be the name of the JavaScript file. The
next elements will be any additional command line arguments.
// print process.argv
process.argv.forEach(function(val, index, array) {
console.log(index + ': ' + val);
});
This will generate:
$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four
## process.execPath
This is the absolute pathname of the executable that started the process.
Example:
/usr/local/bin/node
## process.abort()
This causes node to emit an abort. This will cause node to exit and
generate a core file.
## process.chdir(directory)
Changes the current working directory of the process or throws an exception if that fails.
console.log('Starting directory: ' + process.cwd());
try {
process.chdir('/tmp');
console.log('New directory: ' + process.cwd());
}
catch (err) {
console.log('chdir: ' + err);
}
## process.cwd()
Returns the current working directory of the process.
console.log('Current directory: ' + process.cwd());
## process.env
An object containing the user environment. See environ(7).
## process.exit([code])
Ends the process with the specified `code`. If omitted, exit uses the
'success' code `0`.
To exit with a 'failure' code:
process.exit(1);
The shell that executed node should see the exit code as 1.
## process.getgid()
Note: this function is only available on POSIX platforms (i.e. not Windows)
Gets the group identity of the process. (See getgid(2).)
This is the numerical group id, not the group name.
if (process.getgid) {
console.log('Current gid: ' + process.getgid());
}
## process.setgid(id)
Note: this function is only available on POSIX platforms (i.e. not Windows)
Sets the group identity of the process. (See setgid(2).) This accepts either
a numerical ID or a groupname string. If a groupname is specified, this method
blocks while resolving it to a numerical ID.
if (process.getgid && process.setgid) {
console.log('Current gid: ' + process.getgid());
try {
process.setgid(501);
console.log('New gid: ' + process.getgid());
}
catch (err) {
console.log('Failed to set gid: ' + err);
}
}
## process.getuid()
Note: this function is only available on POSIX platforms (i.e. not Windows)
Gets the user identity of the process. (See getuid(2).)
This is the numerical userid, not the username.
if (process.getuid) {
console.log('Current uid: ' + process.getuid());
}
## process.setuid(id)
Note: this function is only available on POSIX platforms (i.e. not Windows)
Sets the user identity of the process. (See setuid(2).) This accepts either
a numerical ID or a username string. If a username is specified, this method
blocks while resolving it to a numerical ID.
if (process.getuid && process.setuid) {
console.log('Current uid: ' + process.getuid());
try {
process.setuid(501);
console.log('New uid: ' + process.getuid());
}
catch (err) {
console.log('Failed to set uid: ' + err);
}
}
## process.getgroups()
Note: this function is only available on POSIX platforms (i.e. not Windows)
Returns an array with the supplementary group IDs. POSIX leaves it unspecified
if the effective group ID is included but node.js ensures it always is.
## process.setgroups(groups)
Note: this function is only available on POSIX platforms (i.e. not Windows)
Sets the supplementary group IDs. This is a privileged operation, meaning you
need to be root or have the CAP_SETGID capability.
The list can contain group IDs, group names or both.
## process.initgroups(user, extra_group)
Note: this function is only available on POSIX platforms (i.e. not Windows)
Reads /etc/group and initializes the group access list, using all groups of
which the user is a member. This is a privileged operation, meaning you need
to be root or have the CAP_SETGID capability.
`user` is a user name or user ID. `extra_group` is a group name or group ID.
Some care needs to be taken when dropping privileges. Example:
console.log(process.getgroups()); // [ 0 ]
process.initgroups('bnoordhuis', 1000); // switch user
console.log(process.getgroups()); // [ 27, 30, 46, 1000, 0 ]
process.setgid(1000); // drop root gid
console.log(process.getgroups()); // [ 27, 30, 46, 1000 ]
## process.version
A compiled-in property that exposes `NODE_VERSION`.
console.log('Version: ' + process.version);
## process.versions
A property exposing version strings of node and its dependencies.
console.log(process.versions);
Will output:
{ node: '0.4.12',
v8: '3.1.8.26',
ares: '1.7.4',
ev: '4.4',
openssl: '1.0.0e-fips' }
## process.config
An Object containing the JavaScript representation of the configure options
that were used to compile the current node executable. This is the same as
the "config.gypi" file that was produced when running the `./configure` script.
An example of the possible output looks like:
{ target_defaults:
{ cflags: [],
default_configuration: 'Release',
defines: [],
include_dirs: [],
libraries: [] },
variables:
{ host_arch: 'x64',
node_install_npm: 'true',
node_prefix: '',
node_shared_cares: 'false',
node_shared_http_parser: 'false',
node_shared_libuv: 'false',
node_shared_v8: 'false',
node_shared_zlib: 'false',
node_use_dtrace: 'false',
node_use_openssl: 'true',
node_shared_openssl: 'false',
strict_aliasing: 'true',
target_arch: 'x64',
v8_use_snapshot: 'true' } }
## process.kill(pid, [signal])
Send a signal to a process. `pid` is the process id and `signal` is the
string describing the signal to send. Signal names are strings like
'SIGINT' or 'SIGUSR1'. If omitted, the signal will be 'SIGTERM'.
See kill(2) for more information.
Note that just because the name of this function is `process.kill`, it is
really just a signal sender, like the `kill` system call. The signal sent
may do something other than kill the target process.
Example of sending a signal to yourself:
process.on('SIGHUP', function() {
console.log('Got SIGHUP signal.');
});
setTimeout(function() {
console.log('Exiting.');
process.exit(0);
}, 100);
process.kill(process.pid, 'SIGHUP');
## process.pid
The PID of the process.
console.log('This process is pid ' + process.pid);
## process.title
Getter/setter to set what is displayed in 'ps'.
## process.arch
What processor architecture you're running on: `'arm'`, `'ia32'`, or `'x64'`.
console.log('This processor architecture is ' + process.arch);
## process.platform
What platform you're running on:
`'darwin'`, `'freebsd'`, `'linux'`, `'sunos'` or `'win32'`
console.log('This platform is ' + process.platform);
## process.memoryUsage()
Returns an object describing the memory usage of the Node process
measured in bytes.
var util = require('util');
console.log(util.inspect(process.memoryUsage()));
This will generate:
{ rss: 4935680,
heapTotal: 1826816,
heapUsed: 650472 }
`heapTotal` and `heapUsed` refer to V8's memory usage.
## process.nextTick(callback)
On the next loop around the event loop call this callback.
This is *not* a simple alias to `setTimeout(fn, 0)`, it's much more
efficient. It typically runs before any other I/O events fire, but there
are some exceptions. See `process.maxTickDepth` below.
process.nextTick(function() {
console.log('nextTick callback');
});
This is important in developing APIs where you want to give the user the
chance to assign event handlers after an object has been constructed,
but before any I/O has occurred.
function MyThing(options) {
this.setupOptions(options);
process.nextTick(function() {
this.startDoingStuff();
}.bind(this));
}
var thing = new MyThing();
thing.getReadyForStuff();
// thing.startDoingStuff() gets called now, not before.
It is very important for APIs to be either 100% synchronous or 100%
asynchronous. Consider this example:
// WARNING! DO NOT USE! BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
if (arg) {
cb();
return;
}
fs.stat('file', cb);
}
This API is hazardous. If you do this:
maybeSync(true, function() {
foo();
});
bar();
then it's not clear whether `foo()` or `bar()` will be called first.
This approach is much better:
function definitelyAsync(arg, cb) {
if (arg) {
process.nextTick(cb);
return;
}
fs.stat('file', cb);
}
## process.maxTickDepth
* {Number} Default = 1000
Callbacks passed to `process.nextTick` will *usually* be called at the
end of the current flow of execution, and are thus approximately as fast
as calling a function synchronously. Left unchecked, this would starve
the event loop, preventing any I/O from occurring.
Consider this code:
process.nextTick(function foo() {
process.nextTick(foo);
});
In order to avoid the situation where Node is blocked by an infinite
loop of recursive series of nextTick calls, it defers to allow some I/O
to be done every so often.
The `process.maxTickDepth` value is the maximum depth of
nextTick-calling nextTick-callbacks that will be evaluated before
allowing other forms of I/O to occur.
## process.umask([mask])
Sets or reads the process's file mode creation mask. Child processes inherit
the mask from the parent process. Returns the old mask if `mask` argument is
given, otherwise returns the current mask.
var oldmask, newmask = 0644;
oldmask = process.umask(newmask);
console.log('Changed umask from: ' + oldmask.toString(8) +
' to ' + newmask.toString(8));
## process.uptime()
Number of seconds Node has been running.
## process.hrtime()
Returns the current high-resolution real time in a `[seconds, nanoseconds]`
tuple Array. It is relative to an arbitrary time in the past. It is not
related to the time of day and therefore not subject to clock drift. The
primary use is for measuring performance between intervals.
You may pass in the result of a previous call to `process.hrtime()` to get
a diff reading, useful for benchmarks and measuring intervals:
var time = process.hrtime();
// [ 1800216, 927643717 ]
setTimeout(function() {
var diff = process.hrtime(time);
// [ 1, 6962306 ]
console.log('benchmark took %d seconds and %d nanoseconds',
diff[0], diff[1]);
// benchmark took 1 seconds and 6962306 nanoseconds
}, 1000);
[EventEmitter]: events.html#events_class_events_eventemitter
|