---
product: Chilkat
product_version: 11.7.0
language: js
language_label: JavaScript
class: Compression
license: bundle
deprecated: false
reference_html: https://www.chilkatsoft.com/refdoc/jsCompressionRef.html
---
# Chilkat Compression — JavaScript — v11.7.0

> Chilkat 11.7.0 · language=js · class=Compression
> Other versions: replace `11.7.0` in this URL. Other languages: `https://www.chilkatsoft.com/ai-docs/v/11.7.0/<lang>/classes/Compression.md`.
> Language-wide rules (install, unlock, error model, strings/bytes): `https://www.chilkatsoft.com/ai-docs/v/11.7.0/js/guide.md`.

## Purpose

**Compress and decompress bytes, text, files, and streams with a flexible API.**

`Chilkat.Compression` provides a general-purpose API for compressing and decompressing data in memory, files, and streams. It supports multiple algorithms, text charset conversion, encoded output, chunked processing, and streaming operations for large data.

**Multiple algorithms**

Supports `deflate`, `zlib`, `bzip2`, and `lzw`.

**Flexible data types**

Work with byte arrays, strings, `BinData`, `StringBuilder`, files, and streams.

**Chunked processing**

Process data incrementally with `FirstChunk` and `LastChunk` for chunk-aware methods.

**Encoded output**

Return compressed bytes as text using encodings such as `base64`, `hex`, and others.

**Streaming support**

Compress or decompress large files and streams with stable memory usage.

**Compression + encryption**

Combine compression and encryption in file workflows with integrated methods.

**Tip:** For text compression, explicitly set `Charset = "utf-8"` unless another encoding is required. For encoded compressed data, set `EncodingMode` to the desired output format.

For an extended overview, see [Compression Class Overview](https://www.chilkatsoft.com/compression_class_overview.asp). See also [Binary Encodings](https://www.chilkatsoft.com/binary_encodings.asp) for supported encoded output formats.

## Object creation, unlocking and error handling

**Object Creation**

Note: This is intended for running within a [Chilkat.Js embedded JavaScript engine](https://www.chilkatsoft.com/chilkat_javascript_engine.asp).

```
var obj = new CkCompression();
```

Call `Global.UnlockBundle` once at the start of the program, before using this or any other Chilkat class. Any string unlocks a fully functional 30-day trial; a purchased unlock code is used in production. See `guide.md` for the exact code in JavaScript.

How failure is reported depends on the method's return type and is stated in the note under each method below. In every case the diagnostic text is in the `LastErrorText` property of the object whose method was called.

## Members common to every Chilkat class

Documented once per language in `common-members.md`; listed here so this page is self-contained.

| Property | Signature | Access | Meaning |
|---|---|---|---|
| `DebugLogFilePath` | `DebugLogFilePath` | read/write | If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. |
| `LastErrorHtml` | `LastErrorHtml` | read-only | Provides HTML-formatted information about the last called method or property. |
| `LastErrorText` | `LastErrorText` | read-only | Provides plain text information about the last called method or property. |
| `LastErrorXml` | `LastErrorXml` | read-only | Provides XML-formatted information about the last called method or property. |
| `LastMethodSuccess` | `LastMethodSuccess` | read/write | Indicates the success or failure of the most recent method call: `true` means success, `false` means failure. |
| `VerboseLogging` | `VerboseLogging` | read/write | If set to `true`, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. |
| `Version` | `Version` | read-only | Version of the component/library, such as "10.1.0" |

## Member index

| Member | Kind | Signature |
|---|---|---|
| `Algorithm` | property, read/write | `Algorithm` |
| `Charset` | property, read/write | `Charset` |
| `DeflateLevel` | property, read/write | `DeflateLevel` |
| `EncodingMode` | property, read/write | `EncodingMode` |
| `FirstChunk` | property, read/write | `FirstChunk` |
| `LastChunk` | property, read/write | `LastChunk` |
| `UncommonOptions` | property, read/write | `UncommonOptions` |
| `CompressBd` | method | `var success = CompressBd(bd);` |
| `CompressBd2` | method | `var success = CompressBd2(bdIn, bdOut);` |
| `CompressEncryptFile` | method | `var success = CompressEncryptFile(cryptParams, srcPath, destPath);` |
| `CompressFile` | method | `var success = CompressFile(srcPath, destPath);` |
| `CompressSb` | method | `var success = CompressSb(sb, binData);` |
| `CompressStr` | method | `var success = CompressStr(str, bd);` |
| `CompressStringENC` | method | `var strVal = CompressStringENC(str);` |
| `DecompressBd` | method | `var success = DecompressBd(bd);` |
| `DecompressBd2` | method | `var success = DecompressBd2(bdIn, bdOut);` |
| `DecompressFile` | method | `var success = DecompressFile(srcPath, destPath);` |
| `DecompressSb` | method | `var success = DecompressSb(binData, sb);` |
| `DecompressStringENC` | method | `var strVal = DecompressStringENC(encodedCompressedData);` |
| `DecryptDecompressFile` | method | `var success = DecryptDecompressFile(cryptParams, srcPath, destPath);` |

## Properties

### Compression.Algorithm

`Chilkat 11.7.0 · js · Compression · Algorithm · property · read/write`

```javascript
Algorithm
```

· `string`

Specifies the compression algorithm to use. Supported values are `deflate`, `zlib`, `gzip`, `bzip2`, and `lzw`.

The `zlib` option is the deflate algorithm with a zlib header.

The `gzip` option (starting in v11.7.0) is the deflate algorithm in the gzip format (RFC 1952): a gzip header, the deflate data, and a trailer with the CRC-32 and size of the uncompressed data. When decompressing in one call, the CRC-32 and size are checked. Before v11.7.0, `gzip` was not recognized and was treated as `deflate`.

**Note:** `ppmd` is deprecated and should not be used. It was only available on 32-bit systems and specifically used the J variant. New applications should use one of the supported algorithms listed above.

### Compression.Charset

`Chilkat 11.7.0 · js · Compression · Charset · property · read/write`

```javascript
Charset
```

**Full documentation for this property (same in every language):** [How Character Encoding (Charset) Affects Compression and Decompression](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/how_charset_affects_compression.md) · [Full List of Character Encodings Supported by Chilkat](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/charsets_supported_by_chilkat.md)

· `string`

Specifies the character encoding used when converting text to bytes before compression, and bytes back to text after decompression.

The current default is the computer’s ANSI charset, such as Windows-1252 on many Western Windows systems. However, most modern applications should explicitly set this property to `utf-8`.

**Recommendation:** Set `Charset = "utf-8"` unless you specifically need compatibility with another encoding.

### Compression.DeflateLevel

`Chilkat 11.7.0 · js · Compression · DeflateLevel · property · read/write · since 9.5.0.73`

```javascript
DeflateLevel
```

· `int`

Sets the compression level used by the `deflate` and `zlib` algorithms.

- `0` means no compression.
- `9` means maximum compression.
- The default value is `6`.

Higher values may produce smaller output but can require more processing time.

### Compression.EncodingMode

`Chilkat 11.7.0 · js · Compression · EncodingMode · property · read/write`

```javascript
EncodingMode
```

**Full documentation for this property (same in every language):** [Binary Encodings Supported by Chilkat](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/binary_encodings.md)

· `string`

Specifies the text encoding used by methods whose names end in `ENC`, such as `CompressBytesENC` and `DecompressStringENC`.

Compression methods ending in `ENC` return compressed binary data as an encoded string. Decompression methods ending in `ENC` expect the input string to use this same encoding.

Valid values include:

- `base64`
- `hex`
- `url`
- `quoted-printable`

### Compression.FirstChunk

`Chilkat 11.7.0 · js · Compression · FirstChunk · property · read/write · since 11.0.0`

```javascript
FirstChunk
```

· `boolean`

Indicates that the next chunk-aware compression or decompression call is the first chunk in a sequence.

The default value is `true`.

When both `FirstChunk` and `LastChunk` are `true`, the method call is treated as a complete, single-call compression or decompression operation.

### Compression.LastChunk

`Chilkat 11.7.0 · js · Compression · LastChunk · property · read/write · since 11.0.0`

```javascript
LastChunk
```

· `boolean`

Indicates that the next chunk-aware compression or decompression call is the final chunk in a sequence.

The default value is `true`.

When both `FirstChunk` and `LastChunk` are `true`, the input is treated as the complete data set and processed in a single call.

### Compression.UncommonOptions

`Chilkat 11.7.0 · js · Compression · UncommonOptions · property · read/write · since 11.0.0`

```javascript
UncommonOptions
```

· `string`

Provides a way to enable specialized or uncommon behavior. This property normally remains empty.

It may be set to a comma-separated list of keywords.

Supported option:

- `Crypt2CompressHdr` — Duplicates the compression/decompression header behavior used by the deprecated and removed Crypt2 compression functions.

## Methods

### Compression.CompressBd

`Chilkat 11.7.0 · js · Compression · CompressBd · method · since 9.5.0.66`

```javascript
var success = CompressBd(bd);
```

· return: `boolean`; `true` for success, `false` for failure  
· bd: `CkBinData`

Compresses the data contained in a `BinData` object.

The `BinData` object is modified to contain the compressed result.

This method is not `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.CompressBd2

`Chilkat 11.7.0 · js · Compression · CompressBd2 · method · since 11.0.0`

```javascript
var success = CompressBd2(bdIn, bdOut);
```

· return: `boolean`; `true` for success, `false` for failure  
· bdIn: `CkBinData`  
· bdOut: `CkBinData`

Compresses the data in one `BinData` object and appends the compressed output to another `BinData` object.

The input `BinData` is not modified.

This method is `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.CompressEncryptFile

`Chilkat 11.7.0 · js · Compression · CompressEncryptFile · method · since 9.5.0.99`

```javascript
var success = CompressEncryptFile(cryptParams, srcPath, destPath);
```

· return: `boolean`; `true` for success, `false` for failure  
· cryptParams: `CkJsonObject`  
· srcPath: `string`  
· destPath: `string`

Compresses and encrypts a file, writing the result to a destination file.

The compression and encryption are performed internally in streaming mode, so files of any size can be processed without loading the entire file into memory.

Returns true for success, false for failure.

### Compression.CompressFile

`Chilkat 11.7.0 · js · Compression · CompressFile · method`

```javascript
var success = CompressFile(srcPath, destPath);
```

· return: `boolean`; `true` for success, `false` for failure  
· srcPath: `string`  
· destPath: `string`

Compresses a source file and writes the compressed data to a destination file.

The file is processed internally in streaming mode, allowing files of any size to be compressed with stable memory usage.

Returns true for success, false for failure.

### Compression.CompressSb

`Chilkat 11.7.0 · js · Compression · CompressSb · method · since 9.5.0.73`

```javascript
var success = CompressSb(sb, binData);
```

· return: `boolean`; `true` for success, `false` for failure  
· sb: `CkStringBuilder`  
· binData: `CkBinData`

Compresses the text contained in a `StringBuilder` and appends the compressed bytes to a `BinData` object.

Text is converted to bytes according to the `Charset` property.

This method is `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.CompressStr

`Chilkat 11.7.0 · js · Compression · CompressStr · method · since 11.0.0`

```javascript
var success = CompressStr(str, bd);
```

· return: `boolean`; `true` for success, `false` for failure  
· str: `string`  
· bd: `CkBinData`

Compresses a string and appends the compressed bytes to a `BinData` object.

The string is converted to bytes using the charset specified by the `Charset` property.

This method is `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.CompressStringENC

`Chilkat 11.7.0 · js · Compression · CompressStringENC · method`

```javascript
var strVal = CompressStringENC(str);
```

· return: `string`  
· str: `string`

Compresses a string and returns the compressed result as an encoded string.

The string is first converted to bytes using `Charset`, then compressed, and finally encoded according to `EncodingMode`.

This method is not `FirstChunk` / `LastChunk` aware.

Returns `null` on failure

### Compression.DecompressBd

`Chilkat 11.7.0 · js · Compression · DecompressBd · method · since 9.5.0.66`

```javascript
var success = DecompressBd(bd);
```

· return: `boolean`; `true` for success, `false` for failure  
· bd: `CkBinData`

Decompresses the compressed data contained in a `BinData` object.

The `BinData` object is modified to contain the decompressed result.

This method is not `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.DecompressBd2

`Chilkat 11.7.0 · js · Compression · DecompressBd2 · method · since 11.0.0`

```javascript
var success = DecompressBd2(bdIn, bdOut);
```

· return: `boolean`; `true` for success, `false` for failure  
· bdIn: `CkBinData`  
· bdOut: `CkBinData`

Decompresses the data in one `BinData` object and appends the decompressed output to another `BinData` object.

The input `BinData` is not modified.

This method is `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.DecompressFile

`Chilkat 11.7.0 · js · Compression · DecompressFile · method`

```javascript
var success = DecompressFile(srcPath, destPath);
```

· return: `boolean`; `true` for success, `false` for failure  
· srcPath: `string`  
· destPath: `string`

Decompresses a source file and writes the decompressed data to a destination file.

The file is processed internally in streaming mode, allowing files of any size to be decompressed without loading the entire file into memory.

Returns true for success, false for failure.

### Compression.DecompressSb

`Chilkat 11.7.0 · js · Compression · DecompressSb · method · since 9.5.0.73`

```javascript
var success = DecompressSb(binData, sb);
```

· return: `boolean`; `true` for success, `false` for failure  
· binData: `CkBinData`  
· sb: `CkStringBuilder`

Decompresses compressed data from a `BinData` object and appends the resulting text to a `StringBuilder`.

The decompressed bytes are converted to text using the `Charset` property.

This method is `FirstChunk` / `LastChunk` aware.

Returns true for success, false for failure.

### Compression.DecompressStringENC

`Chilkat 11.7.0 · js · Compression · DecompressStringENC · method`

```javascript
var strVal = DecompressStringENC(encodedCompressedData);
```

· return: `string`  
· encodedCompressedData: `string`

Decompresses compressed data supplied as an encoded string and returns the resulting text.

The input string is decoded according to `EncodingMode`, then decompressed. The resulting bytes are converted to text using `Charset`.

This method is not `FirstChunk` / `LastChunk` aware.

Returns `null` on failure

### Compression.DecryptDecompressFile

`Chilkat 11.7.0 · js · Compression · DecryptDecompressFile · method · since 9.5.0.99`

```javascript
var success = DecryptDecompressFile(cryptParams, srcPath, destPath);
```

· return: `boolean`; `true` for success, `false` for failure  
· cryptParams: `CkJsonObject`  
· srcPath: `string`  
· destPath: `string`

Decrypts and decompresses a file, writing the restored data to a destination file.

This is the reverse operation of `CompressEncryptFile`.

Returns true for success, false for failure.

## Events and callbacks

This binding has no event callbacks.

## Related classes

[`BinData`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/js/classes/BinData.md), [`JsonObject`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/js/classes/JsonObject.md), [`StringBuilder`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/js/classes/StringBuilder.md)