ReadonlyclosedReadonlyconnectionAlias of outgoingMessage.socket.
Is true after writable.destroy() has been called.
ReadonlyerroredReturns error if the stream has been destroyed with an error.
Read-only. true if the headers were sent, otherwise false.
Send JSON response.
Examples:
res.json(null);
res.json({ user: 'tj' });
res.status(500).json('oh noes!');
res.status(404).json('I dont have that');
Send JSON response with JSONP callback support.
Examples:
res.jsonp(null);
res.jsonp({ user: 'tj' });
res.status(500).jsonp('oh noes!');
res.status(404).jsonp('I dont have that');
After middleware.init executed, Response will contain req property See: express/lib/middleware/init.js
Send a response.
Examples:
res.send(new Buffer('wahoo'));
res.send({ some: 'json' });
res.send('<p>some html</p>');
res.status(404).send('Sorry, cant find that');
ReadonlysocketReference to the underlying socket. Usually, users will not want to access this property.
After calling outgoingMessage.end(), this property will be nulled.
When using implicit headers (not calling response.writeHead() explicitly),
this property controls the status code that will be sent to the client when
the headers get flushed.
response.statusCode = 404;
After response header was sent to the client, this property indicates the status code which was sent out.
When using implicit headers (not calling response.writeHead() explicitly),
this property controls the status message that will be sent to the client when
the headers get flushed. If this is left as undefined then the standard
message for the status code will be used.
response.statusMessage = 'Not found';
After response header was sent to the client, this property indicates the status message which was sent out.
If set to true, Node.js will check whether the Content-Length header value and the size of the body, in bytes, are equal.
Mismatching the Content-Length header value will result
in an Error being thrown, identified by code:``'ERR_HTTP_CONTENT_LENGTH_MISMATCH'.
ReadonlywritableIs true if it is safe to call writable.write(), which means
the stream has not been destroyed, errored, or ended.
ReadonlywritableNumber of times writable.uncork() needs to be
called in order to fully uncork the stream.
ReadonlywritableIs true after writable.end() has been called. This property
does not indicate whether the data has been flushed, for this use writable.writableFinished instead.
ReadonlywritableIs set to true immediately before the 'finish' event is emitted.
ReadonlywritableReturn the value of highWaterMark passed when creating this Writable.
ReadonlywritableThis property contains the number of bytes (or objects) in the queue
ready to be written. The value provides introspection data regarding
the status of the highWaterMark.
ReadonlywritableIs true if the stream's buffer has been full and stream will emit 'drain'.
ReadonlywritableGetter for the property objectMode of a given Writable stream.
Optional_constructOptional_writevOptional[captureEvent emitter The defined events on documents including:
Event emitter The defined events on documents including:
Event emitter The defined events on documents including:
Event emitter The defined events on documents including:
Event emitter The defined events on documents including:
Event emitter The defined events on documents including:
Event emitter The defined events on documents including:
Adds HTTP trailers (headers but at the end of the message) to the message.
Trailers will only be emitted if the message is chunked encoded. If not, the trailers will be silently discarded.
HTTP requires the Trailer header to be sent to emit trailers,
with a list of header field names in its value, e.g.
message.writeHead(200, { 'Content-Type': 'text/plain',
'Trailer': 'Content-MD5' });
message.write(fileData);
message.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' });
message.end();
Attempting to set a header field name or value that contains invalid characters
will result in a TypeError being thrown.
Appends the specified value to the HTTP response header field. If the header is not already set, it creates the header with the specified value. The value parameter can be a string or an array.
Note: calling res.set() after res.append() will reset the previously-set header value.
Optionalvalue: string | string[]Append a single header value to the header object.
If the value is an array, this is equivalent to calling this method multiple times.
If there were no previous values for the header, this is equivalent to calling outgoingMessage.setHeader(name, value).
Depending of the value of options.uniqueHeaders when the client request or the
server were created, this will end up in the header being sent multiple times or
a single time with values joined using ; .
Header name
Header value
Set Content-Disposition header to attachment with optional filename.
Optionalfilename: stringClear cookie name.
Optionaloptions: CookieOptionsSet Content-Type response header with type through mime.lookup()
when it does not contain "/", or set the Content-Type to type otherwise.
Examples:
res.type('.html');
res.type('html');
res.type('json');
res.type('application/json');
res.type('png');
Set cookie name to val, with the given options.
Options:
maxAge max-age in milliseconds, converted to expiressigned sign the cookiepath defaults to "/"Examples:
// "Remember Me" for 15 minutes res.cookie('rememberme', '1', { expires: new Date(Date.now() + 900000), httpOnly: true });
// save as above res.cookie('rememberme', '1', { maxAge: 900000, httpOnly: true })
The writable.cork() method forces all written data to be buffered in memory.
The buffered data will be flushed when either the uncork or end methods are called.
The primary intent of writable.cork() is to accommodate a situation in which
several small chunks are written to the stream in rapid succession. Instead of
immediately forwarding them to the underlying destination, writable.cork() buffers all the chunks until writable.uncork() is called, which will pass them
all to writable._writev(), if present. This prevents a head-of-line blocking
situation where data is being buffered while waiting for the first small chunk
to be processed. However, use of writable.cork() without implementing writable._writev() may have an adverse effect on throughput.
See also: writable.uncork(), writable._writev().
Destroy the stream. Optionally emit an 'error' event, and emit a 'close' event (unless emitClose is set to false). After this call, the writable
stream has ended and subsequent calls to write() or end() will result in
an ERR_STREAM_DESTROYED error.
This is a destructive and immediate way to destroy a stream. Previous calls to write() may not have drained, and may trigger an ERR_STREAM_DESTROYED error.
Use end() instead of destroy if data should flush before close, or wait for
the 'drain' event before destroying the stream.
Once destroy() has been called any further calls will be a no-op and no
further errors except from _destroy() may be emitted as 'error'.
Implementors should not override this method,
but instead implement writable._destroy().
Optionalerror: ErrorOptional, an error to emit with 'error' event.
Transfer the file at the given path as an attachment.
Optionally providing an alternate attachment filename,
and optional callback fn(err). The callback is invoked
when the data transfer is complete, or when an error has
ocurred. Be sure to check res.headersSent if you plan to respond.
The optional options argument passes through to the underlying res.sendFile() call, and takes the exact same parameters.
This method uses res.sendFile().
Optionalfn: ErrbackOptionalfn: ErrbackOptionalfn: ErrbackSynchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments
to each.
Returns true if the event had listeners, false otherwise.
import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();
// First listener
myEmitter.on('event', function firstListener() {
console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
const parameters = args.join(', ');
console.log(`event with parameters ${parameters} in third listener`);
});
console.log(myEmitter.listeners('event'));
myEmitter.emit('event', 1, 2, 3, 4, 5);
// Prints:
// [
// [Function: firstListener],
// [Function: secondListener],
// [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
Calling the writable.end() method signals that no more data will be written
to the Writable. The optional chunk and encoding arguments allow one
final additional chunk of data to be written immediately before closing the
stream.
Calling the write method after calling end will raise an error.
// Write 'hello, ' and then end with 'world!'.
import fs from 'node:fs';
const file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// Writing more now is not allowed!
Optionalcb: () => voidCalling the writable.end() method signals that no more data will be written
to the Writable. The optional chunk and encoding arguments allow one
final additional chunk of data to be written immediately before closing the
stream.
Calling the write method after calling end will raise an error.
// Write 'hello, ' and then end with 'world!'.
import fs from 'node:fs';
const file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// Writing more now is not allowed!
Optional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer},
{TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.
Optionalcb: () => voidCalling the writable.end() method signals that no more data will be written
to the Writable. The optional chunk and encoding arguments allow one
final additional chunk of data to be written immediately before closing the
stream.
Calling the write method after calling end will raise an error.
// Write 'hello, ' and then end with 'world!'.
import fs from 'node:fs';
const file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// Writing more now is not allowed!
Optional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer},
{TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.
The encoding if chunk is a string
Optionalcb: () => voidReturns an array listing the events for which the emitter has registered
listeners. The values in the array are strings or Symbols.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});
const sym = Symbol('symbol');
myEE.on(sym, () => {});
console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]
Flushes the message headers.
For efficiency reason, Node.js normally buffers the message headers
until outgoingMessage.end() is called or the first chunk of message data
is written. It then tries to pack the headers and data into a single TCP
packet.
It is usually desired (it saves a TCP round-trip), but not when the first
data is not sent until possibly much later. outgoingMessage.flushHeaders() bypasses the optimization and kickstarts the message.
Respond to the Acceptable formats using an obj
of mime-type callbacks.
This method uses req.accepted, an array of
acceptable types ordered by their quality values.
When "Accept" is not present the first callback
is invoked, otherwise the first match is used. When
no match is performed the server responds with
406 "Not Acceptable".
Content-Type is set for you, however if you choose
you may alter this within the callback using res.type()
or res.set('Content-Type', ...).
res.format({ 'text/plain': function(){ res.send('hey'); },
'text/html': function(){
res.send('<p>hey</p>');
},
'appliation/json': function(){
res.send({ message: 'hey' });
}
});
In addition to canonicalized MIME types you may also use extnames mapped to these types:
res.format({ text: function(){ res.send('hey'); },
html: function(){
res.send('<p>hey</p>');
},
json: function(){
res.send({ message: 'hey' });
}
});
By default Express passes an Error
with a .status of 406 to next(err)
if a match is not made. If you provide
a .default callback it will be invoked
instead.
Get value for header field.
Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related HTTP module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.
The object returned by the outgoingMessage.getHeaders() method does
not prototypically inherit from the JavaScript Object. This means that
typical Object methods such as obj.toString(), obj.hasOwnProperty(),
and others are not defined and will not work.
outgoingMessage.setHeader('Foo', 'bar');
outgoingMessage.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
const headers = outgoingMessage.getHeaders();
// headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] }
Optionalvalue: string | string[]Set Link header field with the given links.
Examples:
res.links({ next: 'http://api.example.com/users?page=2', last: 'http://api.example.com/users?page=5' });
Returns the number of listeners listening for the event named eventName.
If listener is provided, it will return how many times the listener is found
in the list of the listeners of the event.
The name of the event being listened for
Optionallistener: FunctionThe event handler function
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => {
console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
Set the location header to url.
Examples:
res.location('/foo/bar').; res.location('http://example.com'); res.location('../login'); // /blog/post/1 -> /blog/login
Mounting:
When an application is mounted and res.location()
is given a path that does not lead with "/" it becomes
relative to the mount-point. For example if the application
is mounted at "/blog", the following would become "/blog/login".
res.location('login');
While the leading slash would result in a location of "/login":
res.location('/login');
Adds the listener function to the end of the listeners array for the event
named eventName. No checks are made to see if the listener has already
been added. Multiple calls passing the same combination of eventName and
listener will result in the listener being added, and called, multiple times.
server.on('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the
event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
The callback function
Adds a one-time listener function for the event named eventName. The
next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the
event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a
The callback function
Adds the listener function to the beginning of the listeners array for the
event named eventName. No checks are made to see if the listener has
already been added. Multiple calls passing the same combination of eventName
and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => {
console.log('someone connected!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
The callback function
Adds a one-timelistener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this
listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => {
console.log('Ah, we have our first user!');
});
Returns a reference to the EventEmitter, so that calls can be chained.
The callback function
Returns a copy of the array of listeners for the event named eventName,
including any wrappers (such as those created by .once()).
import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));
// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];
// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();
// Logs "log once" to the console and removes the listener
logFnWrapper();
emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');
// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
Redirect to the given url with optional response status
defaulting to 302.
The resulting url is determined by res.location(), so
it will play nicely with mounted apps, relative paths, etc.
Examples:
res.redirect('/foo/bar'); res.redirect('http://example.com'); res.redirect(301, 'http://example.com'); res.redirect('../login'); // /blog/post/1 -> /blog/login
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code,
particularly when the EventEmitter instance was created by some other
component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
OptionaleventName: string | symbolRemoves the specified listener from the listener array for the event named eventName.
const callback = (stream) => {
console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified eventName, then removeListener() must be
called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the
time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution
will not remove them fromemit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
const callbackA = () => {
console.log('A');
myEmitter.removeListener('event', callbackB);
};
const callbackB = () => {
console.log('B');
};
myEmitter.on('event', callbackA);
myEmitter.on('event', callbackB);
// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
// A
// B
// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
// A
Because listeners are managed using an internal array, calling this will
change the position indices of any listener registered after the listener
being removed. This will not impact the order in which listeners are called,
but it means that any copies of the listener array as returned by
the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single
event (as in the example below), removeListener() will remove the most
recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events';
const ee = new EventEmitter();
function pong() {
console.log('pong');
}
ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);
ee.emit('ping');
ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
Render view with the given options and optional callback fn.
When a callback function is given a response will not be made
automatically, otherwise a response of 200 and text/html is given.
Options:
cache boolean hinting to the engine it should cachefilename filename of the view being renderedOptionaloptions: objectOptionalcallback: (err: Error, html: string) => voidOptionalcallback: (err: Error, html: string) => voidTransfer the file at the given path.
Automatically sets the Content-Type response header field.
The callback fn(err) is invoked when the transfer is complete
or when an error occurs. Be sure to check res.headersSent
if you wish to attempt responding, as the header and some data
may have already been transferred.
Options:
maxAge defaulting to 0 (can be string converted by ms)root root directory for relative filenamesheaders object of headers to serve with filedotfiles serve dotfiles, defaulting to false; can be "allow" to send themOther options are passed along to send.
Examples:
The following example illustrates how res.sendFile() may
be used as an alternative for the static() middleware for
dynamic situations. The code backing res.sendFile() is actually
the same code, so HTTP cache support etc is identical.
app.get('/user/:uid/photos/:file', function(req, res){
var uid = req.params.uid
, file = req.params.file;
req.user.mayViewFilesFrom(uid, function(yes){
if (yes) {
res.sendFile('/uploads/' + uid + '/' + file);
} else {
res.send(403, 'Sorry! you cant see that.');
}
});
});
Optionalfn: ErrbackOptionalfn: ErrbackSet the response HTTP status code to statusCode and send its string representation as the response body.
http://expressjs.com/4x/api.html#res.sendStatus
Examples:
res.sendStatus(200); // equivalent to res.status(200).send('OK') res.sendStatus(403); // equivalent to res.status(403).send('Forbidden') res.sendStatus(404); // equivalent to res.status(404).send('Not Found') res.sendStatus(500); // equivalent to res.status(500).send('Internal Server Error')
Set header field to val, or pass
an object of header fields.
Examples:
res.set('Foo', ['bar', 'baz']); res.set('Accept', 'application/json'); res.set({ Accept: 'text/plain', 'X-API-Key': 'tobi' });
Aliased as res.header().
Optionalvalue: string | string[]Sets multiple header values for implicit headers. headers must be an instance of
Headers or Map, if a header already exists in the to-be-sent headers, its
value will be replaced.
const headers = new Headers({ foo: 'bar' });
outgoingMessage.setHeaders(headers);
or
const headers = new Map([['foo', 'bar']]);
outgoingMessage.setHeaders(headers);
When headers have been set with outgoingMessage.setHeaders(), they will be
merged with any headers passed to response.writeHead(), with the headers passed
to response.writeHead() given precedence.
// Returns content-type = text/plain
const server = http.createServer((req, res) => {
const headers = new Headers({ 'Content-Type': 'text/html' });
res.setHeaders(headers);
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('ok');
});
By default EventEmitters will print a warning if more than 10 listeners are
added for a particular event. This is a useful default that helps finding
memory leaks. The emitter.setMaxListeners() method allows the limit to be
modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter, so that calls can be chained.
Once a socket is associated with the message and is connected, socket.setTimeout() will be called with msecs as the first parameter.
Optionalcallback: () => voidOptional function to be called when a timeout occurs. Same as binding to the timeout event.
Set status code.
Set Content-Type response header with type through mime.lookup()
when it does not contain "/", or set the Content-Type to type otherwise.
Examples:
res.type('.html');
res.type('html');
res.type('json');
res.type('application/json');
res.type('png');
The writable.uncork() method flushes all data buffered since cork was called.
When using writable.cork() and writable.uncork() to manage the buffering
of writes to a stream, defer calls to writable.uncork() using process.nextTick(). Doing so allows batching of all writable.write() calls that occur within a given Node.js event
loop phase.
stream.cork();
stream.write('some ');
stream.write('data ');
process.nextTick(() => stream.uncork());
If the writable.cork() method is called multiple times on a stream, the
same number of calls to writable.uncork() must be called to flush the buffered
data.
stream.cork();
stream.write('some ');
stream.cork();
stream.write('data ');
process.nextTick(() => {
stream.uncork();
// The data will not be flushed until uncork() is called a second time.
stream.uncork();
});
See also: writable.cork().
Adds the field to the Vary response header, if it is not there already. Examples:
res.vary('User-Agent').render('docs');
The writable.write() method writes some data to the stream, and calls the
supplied callback once the data has been fully handled. If an error
occurs, the callback will be called with the error as its
first argument. The callback is called asynchronously and before 'error' is
emitted.
The return value is true if the internal buffer is less than the highWaterMark configured when the stream was created after admitting chunk.
If false is returned, further attempts to write data to the stream should
stop until the 'drain' event is emitted.
While a stream is not draining, calls to write() will buffer chunk, and
return false. Once all currently buffered chunks are drained (accepted for
delivery by the operating system), the 'drain' event will be emitted.
Once write() returns false, do not write more chunks
until the 'drain' event is emitted. While calling write() on a stream that
is not draining is allowed, Node.js will buffer all written chunks until
maximum memory usage occurs, at which point it will abort unconditionally.
Even before it aborts, high memory usage will cause poor garbage collector
performance and high RSS (which is not typically released back to the system,
even after the memory is no longer required). Since TCP sockets may never
drain if the remote peer does not read the data, writing a socket that is
not draining may lead to a remotely exploitable vulnerability.
Writing data while the stream is not draining is particularly
problematic for a Transform, because the Transform streams are paused
by default until they are piped or a 'data' or 'readable' event handler
is added.
If the data to be written can be generated or fetched on demand, it is
recommended to encapsulate the logic into a Readable and use pipe. However, if calling write() is preferred, it is
possible to respect backpressure and avoid memory issues using the 'drain' event:
function write(data, cb) {
if (!stream.write(data)) {
stream.once('drain', cb);
} else {
process.nextTick(cb);
}
}
// Wait for cb to be called before doing any other write.
write('hello', () => {
console.log('Write completed, do more writes now.');
});
A Writable stream in object mode will always ignore the encoding argument.
Optional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer},
{TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.
Optionalcallback: (error: undefined | null | Error) => voidCallback for when this chunk of data is flushed.
false if the stream wishes for the calling code to wait for the 'drain' event to be emitted before continuing to write additional data; otherwise true.
The writable.write() method writes some data to the stream, and calls the
supplied callback once the data has been fully handled. If an error
occurs, the callback will be called with the error as its
first argument. The callback is called asynchronously and before 'error' is
emitted.
The return value is true if the internal buffer is less than the highWaterMark configured when the stream was created after admitting chunk.
If false is returned, further attempts to write data to the stream should
stop until the 'drain' event is emitted.
While a stream is not draining, calls to write() will buffer chunk, and
return false. Once all currently buffered chunks are drained (accepted for
delivery by the operating system), the 'drain' event will be emitted.
Once write() returns false, do not write more chunks
until the 'drain' event is emitted. While calling write() on a stream that
is not draining is allowed, Node.js will buffer all written chunks until
maximum memory usage occurs, at which point it will abort unconditionally.
Even before it aborts, high memory usage will cause poor garbage collector
performance and high RSS (which is not typically released back to the system,
even after the memory is no longer required). Since TCP sockets may never
drain if the remote peer does not read the data, writing a socket that is
not draining may lead to a remotely exploitable vulnerability.
Writing data while the stream is not draining is particularly
problematic for a Transform, because the Transform streams are paused
by default until they are piped or a 'data' or 'readable' event handler
is added.
If the data to be written can be generated or fetched on demand, it is
recommended to encapsulate the logic into a Readable and use pipe. However, if calling write() is preferred, it is
possible to respect backpressure and avoid memory issues using the 'drain' event:
function write(data, cb) {
if (!stream.write(data)) {
stream.once('drain', cb);
} else {
process.nextTick(cb);
}
}
// Wait for cb to be called before doing any other write.
write('hello', () => {
console.log('Write completed, do more writes now.');
});
A Writable stream in object mode will always ignore the encoding argument.
Optional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer},
{TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.
The encoding, if chunk is a string.
Optionalcallback: (error: undefined | null | Error) => voidCallback for when this chunk of data is flushed.
false if the stream wishes for the calling code to wait for the 'drain' event to be emitted before continuing to write additional data; otherwise true.
Sends an HTTP/1.1 103 Early Hints message to the client with a Link header,
indicating that the user agent can preload/preconnect the linked resources.
The hints is an object containing the values of headers to be sent with
early hints message. The optional callback argument will be called when
the response message has been written.
Example
const earlyHintsLink = '</styles.css>; rel=preload; as=style';
response.writeEarlyHints({
'link': earlyHintsLink,
});
const earlyHintsLinks = [
'</styles.css>; rel=preload; as=style',
'</scripts.js>; rel=preload; as=script',
];
response.writeEarlyHints({
'link': earlyHintsLinks,
'x-trace-id': 'id for diagnostics',
});
const earlyHintsCallback = () => console.log('early hints message sent');
response.writeEarlyHints({
'link': earlyHintsLinks,
}, earlyHintsCallback);
An object containing the values of headers
Optionalcallback: () => voidWill be called when the response message has been written
Sends a response header to the request. The status code is a 3-digit HTTP
status code, like 404. The last argument, headers, are the response headers.
Optionally one can give a human-readable statusMessage as the second
argument.
headers may be an Array where the keys and values are in the same list.
It is not a list of tuples. So, the even-numbered offsets are key values,
and the odd-numbered offsets are the associated values. The array is in the same
format as request.rawHeaders.
Returns a reference to the ServerResponse, so that calls can be chained.
const body = 'hello world';
response
.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain',
})
.end(body);
This method must only be called once on a message and it must
be called before response.end() is called.
If response.write() or response.end() are called before calling
this, the implicit/mutable headers will be calculated and call this function.
When headers have been set with response.setHeader(), they will be merged
with any headers passed to response.writeHead(), with the headers passed
to response.writeHead() given precedence.
If this method is called and response.setHeader() has not been called,
it will directly write the supplied header values onto the network channel
without caching internally, and the response.getHeader() on the header
will not yield the expected result. If progressive population of headers is
desired with potential future retrieval and modification, use response.setHeader() instead.
// Returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('ok');
});
Content-Length is read in bytes, not characters. Use Buffer.byteLength() to determine the length of the body in bytes. Node.js
will check whether Content-Length and the length of the body which has
been transmitted are equal or not.
Attempting to set a header field name or value that contains invalid characters
will result in a [Error][] being thrown.
OptionalstatusMessage: stringOptionalheaders: OutgoingHttpHeaders | OutgoingHttpHeader[]Sends a response header to the request. The status code is a 3-digit HTTP
status code, like 404. The last argument, headers, are the response headers.
Optionally one can give a human-readable statusMessage as the second
argument.
headers may be an Array where the keys and values are in the same list.
It is not a list of tuples. So, the even-numbered offsets are key values,
and the odd-numbered offsets are the associated values. The array is in the same
format as request.rawHeaders.
Returns a reference to the ServerResponse, so that calls can be chained.
const body = 'hello world';
response
.writeHead(200, {
'Content-Length': Buffer.byteLength(body),
'Content-Type': 'text/plain',
})
.end(body);
This method must only be called once on a message and it must
be called before response.end() is called.
If response.write() or response.end() are called before calling
this, the implicit/mutable headers will be calculated and call this function.
When headers have been set with response.setHeader(), they will be merged
with any headers passed to response.writeHead(), with the headers passed
to response.writeHead() given precedence.
If this method is called and response.setHeader() has not been called,
it will directly write the supplied header values onto the network channel
without caching internally, and the response.getHeader() on the header
will not yield the expected result. If progressive population of headers is
desired with potential future retrieval and modification, use response.setHeader() instead.
// Returns content-type = text/plain
const server = http.createServer((req, res) => {
res.setHeader('Content-Type', 'text/html');
res.setHeader('X-Foo', 'bar');
res.writeHead(200, { 'Content-Type': 'text/plain' });
res.end('ok');
});
Content-Length is read in bytes, not characters. Use Buffer.byteLength() to determine the length of the body in bytes. Node.js
will check whether Content-Length and the length of the body which has
been transmitted are equal or not.
Attempting to set a header field name or value that contains invalid characters
will result in a [Error][] being thrown.
Optionalheaders: OutgoingHttpHeaders | OutgoingHttpHeader[]
Is
trueafter'close'has been emitted.