Skip to content
Table of contents

- String decoder
  - Class: `StringDecoder`
    - `new StringDecoder([encoding])`
    - `stringDecoder.end([buffer])`
    - `stringDecoder.write(buffer)`

## String decoder#

Stability: 2 - Stable

Source Code: lib/string_decoder.js

The `node:string_decoder` module provides an API for decoding `Buffer` objects into strings in a manner that preserves encoded multi-byte UTF-8 and UTF-16 characters. It can be accessed using:

    import { StringDecoder } from 'node:string_decoder';const { StringDecoder } = require('node:string_decoder');

The following example shows the basic use of the `StringDecoder` class.

    import { StringDecoder } from 'node:string_decoder';
    import { Buffer } from 'node:buffer';
    const decoder = new StringDecoder('utf8');

    const cent = Buffer.from([0xC2, 0xA2]);
    console.log(decoder.write(cent)); // Prints: ¢

    const euro = Buffer.from([0xE2, 0x82, 0xAC]);
    console.log(decoder.write(euro)); // Prints: €const { StringDecoder } = require('node:string_decoder');
    const decoder = new StringDecoder('utf8');

    const cent = Buffer.from([0xC2, 0xA2]);
    console.log(decoder.write(cent)); // Prints: ¢

    const euro = Buffer.from([0xE2, 0x82, 0xAC]);
    console.log(decoder.write(euro)); // Prints: €

When a `Buffer` instance is written to the `StringDecoder` instance, an internal buffer is used to ensure that the decoded string does not contain any incomplete multibyte characters. These are held in the buffer until the next call to `stringDecoder.write()` or until `stringDecoder.end()` is called.

In the following example, the three UTF-8 encoded bytes of the European Euro symbol (`€`) are written over three separate operations:

    import { StringDecoder } from 'node:string_decoder';
    import { Buffer } from 'node:buffer';
    const decoder = new StringDecoder('utf8');

    decoder.write(Buffer.from([0xE2]));
    decoder.write(Buffer.from([0x82]));
    console.log(decoder.end(Buffer.from([0xAC]))); // Prints: €const { StringDecoder } = require('node:string_decoder');
    const decoder = new StringDecoder('utf8');

    decoder.write(Buffer.from([0xE2]));
    decoder.write(Buffer.from([0x82]));
    console.log(decoder.end(Buffer.from([0xAC]))); // Prints: €

### Class: `StringDecoder`#

#### `new StringDecoder([encoding])`#

Added in: v0.1.99

- `encoding` <string> The character encoding the `StringDecoder` will use. Default: `'utf8'`.

Creates a new `StringDecoder` instance.

#### `stringDecoder.end([buffer])`#

Added in: v0.9.3

- `buffer` <string> | <Buffer> | <TypedArray> | <DataView> The bytes to decode.
- Returns: <string>

Returns any remaining input stored in the internal buffer as a string. Bytes representing incomplete UTF-8 and UTF-16 characters will be replaced with substitution characters appropriate for the character encoding.

If the `buffer` argument is provided, one final call to `stringDecoder.write()` is performed before returning the remaining input. After `end()` is called, the `stringDecoder` object can be reused for new input.

#### `stringDecoder.write(buffer)`#

History

Version | Changes
--- | ---
v8.0.0 | Each invalid character is now replaced by a single replacement character instead of one for each individual byte.
v0.1.99 | Added in: v0.1.99

- `buffer` <string> | <Buffer> | <TypedArray> | <DataView> The bytes to decode.
- Returns: <string>

Returns a decoded string, ensuring that any incomplete multibyte characters at the end of the `Buffer`, or `TypedArray`, or `DataView` are omitted from the returned string and stored in an internal buffer for the next call to `stringDecoder.write()` or `stringDecoder.end()`.