xref: /third_party/node/doc/api/tty.md

# TTY

<!--introduced_in=v0.10.0-->

> Stability: 2 - Stable

<!-- source_link=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:

```js
const tty = require('node: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`:

```console
$ 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`

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* 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`

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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`

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A `boolean` that is always `true` for `tty.ReadStream` instances.

### `readStream.setRawMode(mode)`

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* `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. <kbd>Ctrl</kbd>+<kbd>C</kbd> will no longer cause a `SIGINT` when
in this mode.

## Class: `tty.WriteStream`

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* 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'`

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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.

```js
process.stdout.on('resize', () => {
  console.log('screen size has changed!');
  console.log(`${process.stdout.columns}x${process.stdout.rows}`);
});
```

### `writeStream.clearLine(dir[, callback])`

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    description: The stream's write() callback and return value are exposed.
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* `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])`

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    description: The stream's write() callback and return value are exposed.
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* `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`

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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])`

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    description: The stream's write() callback and return value are exposed.
-->

* `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])`

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* `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()`

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* 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])`

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* `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()`][].

```js
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`

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A `boolean` that is always `true`.

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

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added: v0.7.7
changes:
  - version: v12.7.0
    pr-url: https://github.com/nodejs/node/pull/28721
    description: The stream's write() callback and return value are exposed.
-->

* `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`

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

## `tty.isatty(fd)`

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* `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.

[`process.stderr`]: process.md#processstderr
[`process.stdin`]: process.md#processstdin
[`process.stdout`]: process.md#processstdout
[`writeStream.getColorDepth()`]: #writestreamgetcolordepthenv