ReadonlycursorThe cursor position relative to rl.line.
This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered.
ReadonlylineThe current input data being processed by node.
This can be used when collecting input from a TTY stream to retrieve the
current value that has been processed thus far, prior to the line event
being emitted. Once the line event has been emitted, this property will
be an empty string.
Be aware that modifying the value during the instance runtime may have
unintended consequences if rl.cursor is not also controlled.
If not using a TTY stream for input, use the 'line' event.
One possible use case would be as follows:
const values = ['lorem ipsum', 'dolor sit amet'];
const rl = readline.createInterface(process.stdin);
const showResults = debounce(() => {
console.log(
'\n',
values.filter((val) => val.startsWith(rl.line)).join(' '),
);
}, 300);
process.stdin.on('keypress', (c, k) => {
showResults();
});
ReadonlyterminalOptional[captureevents.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
events.EventEmitter
The rl.close() method closes the Interface instance and
relinquishes control over the input and output streams. When called,
the 'close' event will be emitted.
Calling rl.close() does not immediately stop other events (including 'line')
from being emitted by the Interface instance.
Synchronously 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
Returns 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) ]
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] ]
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
The rl.prompt() method writes the Interface instances configuredprompt to a new line in output in order to provide a user with a new
location at which to provide input.
When called, rl.prompt() will resume the input stream if it has been
paused.
If the Interface was created with output set to null or undefined the prompt is not written.
OptionalpreserveCursor: booleanIf true, prevents the cursor placement from being reset to 0.
The rl.question() method displays the query by writing it to the output,
waits for user input to be provided on input, then invokes the callback function passing the provided input as the first argument.
When called, rl.question() will resume the input stream if it has been
paused.
If the Interface was created with output set to null or undefined the query is not written.
If the question is called after rl.close(), it returns a rejected promise.
Example usage:
const answer = await rl.question('What is your favorite food? ');
console.log(`Oh, so your favorite food is ${answer}`);
Using an AbortSignal to cancel a question.
const signal = AbortSignal.timeout(10_000);
signal.addEventListener('abort', () => {
console.log('The food question timed out');
}, { once: true });
const answer = await rl.question('What is your favorite food? ', { signal });
console.log(`Oh, so your favorite food is ${answer}`);
A statement or query to write to output, prepended to the prompt.
A promise that is fulfilled with the user's input in response to the query.
The rl.question() method displays the query by writing it to the output,
waits for user input to be provided on input, then invokes the callback function passing the provided input as the first argument.
When called, rl.question() will resume the input stream if it has been
paused.
If the Interface was created with output set to null or undefined the query is not written.
If the question is called after rl.close(), it returns a rejected promise.
Example usage:
const answer = await rl.question('What is your favorite food? ');
console.log(`Oh, so your favorite food is ${answer}`);
Using an AbortSignal to cancel a question.
const signal = AbortSignal.timeout(10_000);
signal.addEventListener('abort', () => {
console.log('The food question timed out');
}, { once: true });
const answer = await rl.question('What is your favorite food? ', { signal });
console.log(`Oh, so your favorite food is ${answer}`);
A statement or query to write to output, prepended to the prompt.
A promise that is fulfilled with the user's input in response to the query.
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');
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.
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.
The rl.write() method will write either data or a key sequence identified
by key to the output. The key argument is supported only if output is
a TTY text terminal. See TTY keybindings for a list of key
combinations.
If key is specified, data is ignored.
When called, rl.write() will resume the input stream if it has been
paused.
If the Interface was created with output set to null or undefined the data and key are not written.
rl.write('Delete this!');
// Simulate Ctrl+U to delete the line written previously
rl.write(null, { ctrl: true, name: 'u' });
The rl.write() method will write the data to the readline Interface's input as if it were provided by the user.
Optionalkey: KeyThe rl.write() method will write either data or a key sequence identified
by key to the output. The key argument is supported only if output is
a TTY text terminal. See TTY keybindings for a list of key
combinations.
If key is specified, data is ignored.
When called, rl.write() will resume the input stream if it has been
paused.
If the Interface was created with output set to null or undefined the data and key are not written.
rl.write('Delete this!');
// Simulate Ctrl+U to delete the line written previously
rl.write(null, { ctrl: true, name: 'u' });
The rl.write() method will write the data to the readline Interface's input as if it were provided by the user.
Instances of the
readlinePromises.Interfaceclass are constructed using thereadlinePromises.createInterface()method. Every instance is associated with a singleinputReadablestream and a singleoutputWritablestream. Theoutputstream is used to print prompts for user input that arrives on, and is read from, theinputstream.Since
v17.0.0