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TTY

Stability: 2 - Stable

The 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('tty');

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

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.

Class: tty.ReadStream

  • Extends: {net.Socket}

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. Defaults to false.

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.
  • Returns: {this} The read stream instance.

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.

Class: tty.WriteStream

  • Extends: {net.Socket}

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.

Event: '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}`);
});

writeStream.clearLine(dir[, callback])

  • dir {number}
    • -1: to the left from cursor
    • 1: to the right from cursor
    • 0: the entire line
  • callback {Function} Invoked once the operation completes.
  • Returns: {boolean} 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.
  • Returns: {boolean} 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.
  • Returns: {boolean} 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: {number}

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.

  • 2 colors: FORCE_COLOR = 0 (Disables colors)
  • 16 colors: FORCE_COLOR = 1
  • 256 colors: FORCE_COLOR = 2
  • 16,777,216 colors: FORCE_COLOR = 3

Disabling color support is also possible by using the NO_COLOR and NODE_DISABLE_COLORS environment variables.

writeStream.getWindowSize()

  • Returns: {number[]}

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: {boolean}

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).

writeStream.isTTY

A boolean that is always true.

writeStream.moveCursor(dx, dy[, callback])

  • dx {number}
  • dy {number}
  • callback {Function} Invoked once the operation completes.
  • Returns: {boolean} 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)

  • fd {number} A numeric file descriptor
  • Returns: {boolean}

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.