In Nodejs, when I console.log a req object, what does [Circular] mean?
Here's an example console.log(req) against a basic nodejs example. Notice the request.socket._readWatcher.socket is a [Circular]. Does that mean it refers to itself? How can I dereference that?
{ socket:
{ bufferSize: 0,
fd: 7,
type: 'tcp4',
allowHalfOpen: true,
_readWatcher:
{ socket: [Circular],
callback: [Function: onReadable] },
destroyed: false,
readable: true,
_writeQueue: [],
_writeQueueEncoding: [],
_writeQueueFD: [],
_writeQueueCallbacks: [],
_writeWatcher:
{ socket: [Circular],
callback: [Function: onWritable] },
writable: true,
_writeImpl: [Function],
_readImpl: [Function],
_shutdownImpl: [Function],
remoteAddress: '127.0.1.1',
remotePort: 40407,
server:
{ connections: 1,
allowHalfOpen: true,
watcher: [Object],
_events: [Object],
httpAllowHalfOpen: false,
type: 'tcp4',
fd: 5 },
ondrain: [Function],
_idleTimeout: 120000,
_idleNext:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idlePrev:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idleStart: Sun, 15 May 2011 01:18:50 GMT,
_events:
{ timeout: [Function],
error: [Function],
close: [Function] },
ondata: [Function],
onend: [Function],
_httpMessage:
{ output: [],
outputEncodings: [],
writable: true,
_last: false,
chunkedEncoding: true,
shouldKeepAlive: true,
useChunkedEncodingByDefault: true,
_hasBody: true,
_trailer: '',
finished: false,
socket: [Circular],
connection: [Circular],
_events: [Object],
_header: 'HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nConnection: keep-alive\r\nTransfer-Encoding: chunked\r\n\r\n',
_headerSent: false } },
connection:
{ bufferSize: 0,
fd: 7,
type: 'tcp4',
allowHalfOpen: true,
_readWatcher:
{ socket: [Circular],
callback: [Function: onReadable] },
destroyed: false,
readable: true,
_writeQueue: [],
_writeQueueEncoding: [],
_writeQueueFD: [],
_writeQueueCallbacks: [],
_writeWatcher:
{ socket: [Circular],
callback: [Function: onWritable] },
writable: true,
_writeImpl: [Function],
_readImpl: [Function],
_shutdownImpl: [Function],
remoteAddress: '127.0.1.1',
remotePort: 40407,
server:
{ connections: 1,
allowHalfOpen: true,
watcher: [Object],
_events: [Object],
httpAllowHalfOpen: false,
type: 'tcp4',
fd: 5 },
ondrain: [Function],
_idleTimeout: 120000,
_idleNext:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idlePrev:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idleStart: Sun, 15 May 2011 01:18:50 GMT,
_events:
{ timeout: [Function],
error: [Function],
close: [Function] },
ondata: [Function],
onend: [Function],
_httpMessage:
{ output: [],
outputEncodings: [],
writable: true,
_last: false,
chunkedEncoding: true,
shouldKeepAlive: true,
useChunkedEncodingByDefault: true,
_hasBody: true,
_trailer: '',
finished: false,
socket: [Circular],
connection: [Circular],
_events: [Object],
_header: 'HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nConnection: keep-alive\r\nTransfer-Encoding: chunked\r\n\r\n',
_headerSent: false } },
httpVersion: '1.1',
complete: false,
headers:
{ 'user-agent': 'curl/7.21.0 (x86_64-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18',
host: 'uh-uh-uh-I-aint-telling',
accept: '*/*' },
trailers: {},
readable: true,
url: '/',
method: 'GET',
statusCode: null,
client:
{ bufferSize: 0,
fd: 7,
type: 'tcp4',
allowHalfOpen: true,
_readWatcher:
{ socket: [Circular],
callback: [Function: onReadable] },
destroyed: false,
readable: true,
_writeQueue: [],
_writeQueueEncoding: [],
_writeQueueFD: [],
_writeQueueCallbacks: [],
_writeWatcher:
{ socket: [Circular],
callback: [Function: onWritable] },
writable: true,
_writeImpl: [Function],
_readImpl: [Function],
_shutdownImpl: [Function],
remoteAddress: '127.0.1.1',
remotePort: 40407,
server:
{ connections: 1,
allowHalfOpen: true,
watcher: [Object],
_events: [Object],
httpAllowHalfOpen: false,
type: 'tcp4',
fd: 5 },
ondrain: [Function],
_idleTimeout: 120000,
_idleNext:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idlePrev:
{ repeat: 120,
_idleNext: [Circular],
_idlePrev: [Circular],
callback: [Function] },
_idleStart: Sun, 15 May 2011 01:18:50 GMT,
_events:
{ timeout: [Function],
error: [Function],
close: [Function] },
ondata: [Function],
onend: [Function],
_httpMessage:
{ output: [],
outputEncodings: [],
writable: true,
_last: false,
chunkedEncoding: true,
shouldKeepAlive: true,
useChunkedEncodingByDefault: true,
_hasBody: true,
_trailer: '',
finished: false,
socket: [Circular],
connection: [Circular],
_events: [Object],
_header: 'HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nConnection: keep-alive\r\nTransfer-Encoding: chunked\r\n\r\n',
_headerSent: false } },
httpVersionMajor: 1,
httpVersionMinor: 1,
upgrade: false }
Since I apparently wasn't as clear as I could have been, how can I dereference what element is being referenced circularly? Is it always the parent element?
Also of note, last night I learned about the Utils class, and the inspect method. Which will probably give me way more information about this than I should reasonably want to know ;)
A circular dependency occurs when two classes depend on each other.
log() function from console class of Node. js is used to display the messages on the console. It prints to stdout with newline. Parameter: This function contains multiple parameters which are to be printed.
A circular reference occurs if two separate objects pass references to each other. In older browsers circular references were a cause of memory leaks. With improvements in Garbage collection algorithms, which can now handle cycles and cyclic dependencies fine, this is no longer an issue.
It's a circular reference. That's all.
Example:
a.b = a
Now log it:
[Object a] {
b: [Object a] {
b: [Object a] {
b: [Object a] {
b: [Object a] {
b: [Object a] {
b: [Object a] {
... welcome to recursion!
}
}
}
}
}
}
}
It will never end, and the log
call will produce a stack overflow and that's it. Node detects those and gives out the circular reference text instead.
[Circular]
simply means circular reference.
var o = {
"self": o
}
Is shown as
{
"self": [Circular]
}
It could be shown as
{
"self": {
"self": {
"self": {
...
}
}
}
}
In your case socket
is the outer socket.
And _idleNext
and _idlePrev
also point to the outer ones.
Update
_idleNext: // This one!
{ repeat: 120,
_idleNext: [Circular],
{ socket: // this one!
{ bufferSize: 0,
fd: 7,
type: 'tcp4',
allowHalfOpen: true,
_readWatcher:
{ socket: [Circular],
callback: [Function: onReadable] },
destroyed: false,
readable: true,
_writeQueue: [],
_writeQueueEncoding: [],
_writeQueueFD: [],
_writeQueueCallbacks: [],
_writeWatcher:
{ socket: [Circular],
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