Source Code: lib/tty.js
The node:tty
module provides the tty.ReadStream
and tty.WriteStream
classes. In most cases, it will not be necessary or possible to use this module directly. However, it can be accessed using:
const tty = require('node:tty'); copy
When Node.js detects that it is being run with a text terminal ("TTY") attached, process.stdin
will, by default, be initialized as an instance of tty.ReadStream
and both process.stdout
and process.stderr
will, by default, be instances of tty.WriteStream
. The preferred method of determining whether Node.js is being run within a TTY context is to check that the value of the process.stdout.isTTY
property is true
:
$ node -p -e "Boolean(process.stdout.isTTY)" true $ node -p -e "Boolean(process.stdout.isTTY)" | cat false copy
In most cases, there should be little to no reason for an application to manually create instances of the tty.ReadStream
and tty.WriteStream
classes.
tty.ReadStream
Represents the readable side of a TTY. In normal circumstances process.stdin
will be the only tty.ReadStream
instance in a Node.js process and there should be no reason to create additional instances.
readStream.isRaw
A boolean
that is true
if the TTY is currently configured to operate as a raw device.
This flag is always false
when a process starts, even if the terminal is operating in raw mode. Its value will change with subsequent calls to setRawMode
.
readStream.isTTY
A boolean
that is always true
for tty.ReadStream
instances.
readStream.setRawMode(mode)
mode
<boolean> If true
, configures the tty.ReadStream
to operate as a raw device. If false
, configures the tty.ReadStream
to operate in its default mode. The readStream.isRaw
property will be set to the resulting mode.Allows configuration of tty.ReadStream
so that it operates as a raw device.
When in raw mode, input is always available character-by-character, not including modifiers. Additionally, all special processing of characters by the terminal is disabled, including echoing input characters. Ctrl+C will no longer cause a SIGINT
when in this mode.
tty.WriteStream
Represents the writable side of a TTY. In normal circumstances, process.stdout
and process.stderr
will be the only tty.WriteStream
instances created for a Node.js process and there should be no reason to create additional instances.
'resize'
The 'resize'
event is emitted whenever either of the writeStream.columns
or writeStream.rows
properties have changed. No arguments are passed to the listener callback when called.
process.stdout.on('resize', () => { console.log('screen size has changed!'); console.log(`${process.stdout.columns}x${process.stdout.rows}`); }); copy
writeStream.clearLine(dir[, callback])
dir
<number> -1
: to the left from cursor1
: to the right from cursor0
: the entire linecallback
<Function> Invoked once the operation completes.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
.writeStream.clearLine()
clears the current line of this WriteStream
in a direction identified by dir
.
writeStream.clearScreenDown([callback])
callback
<Function> Invoked once the operation completes.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
.writeStream.clearScreenDown()
clears this WriteStream
from the current cursor down.
writeStream.columns
A number
specifying the number of columns the TTY currently has. This property is updated whenever the 'resize'
event is emitted.
writeStream.cursorTo(x[, y][, callback])
x
<number>
y
<number>
callback
<Function> Invoked once the operation completes.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
.writeStream.cursorTo()
moves this WriteStream
's cursor to the specified position.
writeStream.getColorDepth([env])
env
<Object> An object containing the environment variables to check. This enables simulating the usage of a specific terminal. Default: process.env
.Returns:
1
for 2,4
for 16,8
for 256,24
for 16,777,216 colors supported.Use this to determine what colors the terminal supports. Due to the nature of colors in terminals it is possible to either have false positives or false negatives. It depends on process information and the environment variables that may lie about what terminal is used. It is possible to pass in an env
object to simulate the usage of a specific terminal. This can be useful to check how specific environment settings behave.
To enforce a specific color support, use one of the below environment settings.
FORCE_COLOR = 0
(Disables colors)FORCE_COLOR = 1
FORCE_COLOR = 2
FORCE_COLOR = 3
Disabling color support is also possible by using the NO_COLOR
and NODE_DISABLE_COLORS
environment variables.
writeStream.getWindowSize()
writeStream.getWindowSize()
returns the size of the TTY corresponding to this WriteStream
. The array is of the type [numColumns, numRows]
where numColumns
and numRows
represent the number of columns and rows in the corresponding TTY.
writeStream.hasColors([count][, env])
count
<integer> The number of colors that are requested (minimum 2). Default: 16.env
<Object> An object containing the environment variables to check. This enables simulating the usage of a specific terminal. Default: process.env
.Returns true
if the writeStream
supports at least as many colors as provided in count
. Minimum support is 2 (black and white).
This has the same false positives and negatives as described in writeStream.getColorDepth()
.
process.stdout.hasColors(); // Returns true or false depending on if `stdout` supports at least 16 colors. process.stdout.hasColors(256); // Returns true or false depending on if `stdout` supports at least 256 colors. process.stdout.hasColors({ TMUX: '1' }); // Returns true. process.stdout.hasColors(2 ** 24, { TMUX: '1' }); // Returns false (the environment setting pretends to support 2 ** 8 colors). copy
writeStream.isTTY
A boolean
that is always true
.
writeStream.moveCursor(dx, dy[, callback])
dx
<number>
dy
<number>
callback
<Function> Invoked once the operation completes.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
.writeStream.moveCursor()
moves this WriteStream
's cursor relative to its current position.
writeStream.rows
A number
specifying the number of rows the TTY currently has. This property is updated whenever the 'resize'
event is emitted.
tty.isatty(fd)
The tty.isatty()
method returns true
if the given fd
is associated with a TTY and false
if it is not, including whenever fd
is not a non-negative integer.
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https://nodejs.org/api/tty.html