nodejs/doc/api/tty.md

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

The tty.ReadStream class is a subclass of net.Socket that 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)

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. Note that CTRL+C will no longer cause a SIGINT when in this 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.

Class: tty.WriteStream

The tty.WriteStream class is a subclass of net.Socket that 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.columns

A number specifying the number of columns the TTY currently has. This property is updated whenever the 'resize' event is emitted.

writeStream.isTTY

A boolean that is always true.

writeStream.rows

A number specifying the number of rows the TTY currently has. This property is updated whenever the 'resize' event is emitted.

writeStream.getColorDepth([env])

• env {Object} An object containing the environment variables to check. 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. To enforce a specific behavior without relying on process.env it is possible to pass in an object with different settings.

Use the NODE_DISABLE_COLORS environment variable to enforce this function to always return 1.

tty.isatty(fd)

• fd {number} A numeric file descriptor

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.