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

> Chilkat 11.7.0 · language=js · class=Gzip
> Other versions: replace `11.7.0` in this URL. Other languages: `https://www.chilkatsoft.com/ai-docs/v/11.7.0/<lang>/classes/Gzip.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, decompress, inspect, and convert GZIP data in files or memory.**

`Chilkat.Gzip` provides GZIP compression and decompression for file-based and in-memory workflows. It can compress and uncompress files, strings, byte arrays, `BinData`, and encoded data such as Base64 or hex. It also supports `.tar.gz` extraction, gzip metadata such as original filename, timestamp, and comments, and inspection of GZIP header information without fully expanding the compressed data.

**File compression**

Compress files to `.gz`, uncompress `.gz` files, and write decompressed output directly to disk.

**Memory-based data**

Work with byte arrays and `Chilkat.BinData` for applications that need compression or decompression without temporary files.

**String workflows**

Compress and uncompress strings with explicit charset handling for text data that must round-trip correctly.

**Encoded GZIP data**

Handle GZIP data represented as Base64, hex, or other supported encoded forms when binary data must be carried as text.

**GZIP metadata**

Set or inspect metadata such as original filename, modified time, comments, and extra data stored in the GZIP header.

**Tar-gzip and XFDL**

Extract `.tar.gz` archives and decode XFDL content that uses gzip-related encodings.

**Common pattern:** Use `Gzip` when the data is a single GZIP stream, a `.gz` file, or a `.tar.gz` archive. For ZIP archives, use `Chilkat.Zip`; for raw deflate or zlib-style compression, use `Chilkat.Compression`.

For an extended overview, see [Gzip Class Overview](https://www.chilkatsoft.com/gzip_overview.asp).

## 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 CkGzip();
```

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 |
|---|---|---|
| `AbortCurrent` | property, read/write | `AbortCurrent` |
| `Comment` | property, read/write | `Comment` |
| `CompressionLevel` | property, read/write | `CompressionLevel` |
| `Filename` | property, read/write | `Filename` |
| `LastModStr` | property, read/write | `LastModStr` |
| `UseCurrentDate` | property, read/write | `UseCurrentDate` |
| `CompressBd` | method | `var success = CompressBd(binDat);` |
| `CompressFile` | method | `var success = CompressFile(srcPath, destPath);` |
| `CompressFile2` | method | `var success = CompressFile2(srcPath, embeddedFilename, destPath);` |
| `CompressFileBd` | method | `var success = CompressFileBd(filePath, bd);` |
| `CompressSb` | method | `var success = CompressSb(sb, charset, bd);` |
| `CompressStringENC` | method | `var strVal = CompressStringENC(inStr, charset, encoding);` |
| `CompressStringToFile` | method | `var success = CompressStringToFile(inStr, destCharset, destPath);` |
| `GetGzipInfo` | method | `var success = GetGzipInfo(filePath, json);` |
| `GetGzipInfoBd` | method | `var success = GetGzipInfoBd(bd, json);` |
| `IsGzip` | method | `var boolVal = IsGzip(bd);` |
| `SetDt` | method | `var success = SetDt(dt);` |
| `SetExtraData` | method | `var success = SetExtraData(encodedData, encoding);` |
| `UncompressBd` | method | `var success = UncompressBd(binDat);` |
| `UncompressBdToFile` | method | `var success = UncompressBdToFile(bd, filePath);` |
| `UncompressFile` | method | `var success = UncompressFile(srcPath, destPath);` |
| `UncompressFileToString` | method | `var strVal = UncompressFileToString(srcPath, charset);` |
| `UncompressStringENC` | method | `var strVal = UncompressStringENC(inStr, charset, encoding);` |
| `UnTarGz` | method | `var success = UnTarGz(gzPath, destDir, bNoAbsolute);` |
| `XfdlToXml` | method | `var strVal = XfdlToXml(xfldData);` |

## Properties

### Gzip.AbortCurrent

`Chilkat 11.7.0 · js · Gzip · AbortCurrent · property · read/write · since 9.5.0.58`

```javascript
AbortCurrent
```

· `boolean`

Set this property to `true` to request that the currently running operation be aborted. This is useful for long-running operations such as large file compression or decompression. Methods that complete quickly are generally not affected.

If no method is currently running, the property is automatically reset to `false` when the next method begins. After an abort occurs, it is also reset to `false`. Both synchronous and asynchronous operations can be aborted. For synchronous calls, another thread must set this property.

### Gzip.Comment

`Chilkat 11.7.0 · js · Gzip · Comment · property · read/write`

```javascript
Comment
```

· `string`

An optional comment to embed in the Gzip file when a `Compress*` method is called.

### Gzip.CompressionLevel

`Chilkat 11.7.0 · js · Gzip · CompressionLevel · property · read/write · since 9.5.0.50`

```javascript
CompressionLevel
```

· `int`

Controls the compression level used when creating Gzip data. The value can range from `0` to `9`.

- `0` = no compression
- `9` = maximum compression

The default value is `6`, which is a typical balance between compression size and speed. Higher levels may take significantly more CPU time while producing only slightly smaller output, depending on the data.

### Gzip.Filename

`Chilkat 11.7.0 · js · Gzip · Filename · property · read/write`

```javascript
Filename
```

· `string`

The filename to embed in the Gzip file when a `Compress*` method is called. Some Gzip extraction tools use this embedded filename as the default output filename.

### Gzip.LastModStr

`Chilkat 11.7.0 · js · Gzip · LastModStr · property · read/write`

```javascript
LastModStr
```

· `string`

Specifies the last-modified date/time to embed in the Gzip file when a `Compress*` method is called.

The value must be provided as an RFC 822 formatted date/time string.

**Example:**

```
Sun, 12 Apr 2026 12:45:26 GMT
```

If this property is not set, the current system date/time is used automatically.

### Gzip.UseCurrentDate

`Chilkat 11.7.0 · js · Gzip · UseCurrentDate · property · read/write`

```javascript
UseCurrentDate
```

· `boolean`

Controls the last-modified date/time assigned to files created by `Uncompress*` methods.

When set to `true`, the extracted file uses the current date/time instead of the date/time stored in the Gzip data.

## Methods

### Gzip.CompressBd

`Chilkat 11.7.0 · js · Gzip · CompressBd · method · since 9.5.0.67`

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

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

Compresses the contents of a `BinData` object in place, replacing the original data with Gzip-compressed data.

Returns true for success, false for failure.

### Gzip.CompressFile

`Chilkat 11.7.0 · js · Gzip · CompressFile · method`

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

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

Compresses a file and writes the result as a Gzip file, typically with a `.gz` extension.

Returns true for success, false for failure.

### Gzip.CompressFile2

`Chilkat 11.7.0 · js · Gzip · CompressFile2 · method`

```javascript
var success = CompressFile2(srcPath, embeddedFilename, destPath);
```

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

Compresses a file and writes the result as a Gzip file, while allowing a different filename to be embedded inside the Gzip data.

The `inFilename` parameter is the actual file on disk. The `srcPath` parameter is the filename stored in the Gzip header and may be used by extraction tools as the output filename.

Returns true for success, false for failure.

### Gzip.CompressFileBd

`Chilkat 11.7.0 · js · Gzip · CompressFileBd · method · since 11.0.0`

```javascript
var success = CompressFileBd(filePath, bd);
```

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

Compresses a file and stores the resulting Gzip data in a `BinData` object.

The compressed output is held in memory. The maximum compressed size is 4 GB.

Returns true for success, false for failure.

### Gzip.CompressSb

`Chilkat 11.7.0 · js · Gzip · CompressSb · method · since 11.0.0`

```javascript
var success = CompressSb(sb, charset, bd);
```

· return: `boolean`; `true` for success, `false` for failure  
· sb: `CkStringBuilder`  
· charset: `string`  
· bd: `CkBinData`

Compresses the text contained in a `StringBuilder` and writes the Gzip-compressed result to a `BinData` object.

Before compression, the string is converted to bytes using the specified character set, such as `utf-8`, `iso-8859-1`, or `shift_JIS`.

Returns true for success, false for failure.

### Gzip.CompressStringENC

`Chilkat 11.7.0 · js · Gzip · CompressStringENC · method`

```javascript
var strVal = CompressStringENC(inStr, charset, encoding);
```

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

· return: `string`  
· inStr: `string`  
· charset: `string`  
· encoding: `string`

Compresses a string and returns the Gzip-compressed data as an encoded string.

The input string is first converted to bytes using the specified character set. The compressed binary data is then encoded using the requested encoding, such as `base64`, `hex`, `url`, `base32`, or quoted-printable.

Returns `null` on failure

### Gzip.CompressStringToFile

`Chilkat 11.7.0 · js · Gzip · CompressStringToFile · method`

```javascript
var success = CompressStringToFile(inStr, destCharset, destPath);
```

**Full documentation for this method (same in every language):** [Full List of Charset Names](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/charsets_supported_by_chilkat.md)

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

Compresses a string and writes the resulting Gzip data to a file.

The string is first converted to bytes using the character set specified by `destCharset`.

Returns true for success, false for failure.

### Gzip.GetGzipInfo

`Chilkat 11.7.0 · js · Gzip · GetGzipInfo · method · since 11.5.0`

```javascript
var success = GetGzipInfo(filePath, json);
```

· return: `boolean`; `true` for success, `false` for failure  
· filePath: `string`  
· json: `CkJsonObject`

Retrieves metadata stored in a Gzip file and returns the information in a `JsonObject`.

The metadata is returned using the following JSON structure:

```
{
  "extraData": "AAECAw==",
  "filename": "example.txt",
  "comment": "This is the comment"
}
```

- **filename** – the original filename embedded in the Gzip file (if present)
- **comment** – an optional descriptive comment (if present)
- **extraData** – optional additional binary data, returned as a Base64-encoded string

Any of these fields may be omitted if they were not included when the Gzip file was created.

Returns true for success, false for failure.

### Gzip.GetGzipInfoBd

`Chilkat 11.7.0 · js · Gzip · GetGzipInfoBd · method · since 11.5.0`

```javascript
var success = GetGzipInfoBd(bd, json);
```

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

Retrieves metadata stored in Gzip data contained within a `BinData` object and returns the information in a `JsonObject`.

The metadata is returned using the same JSON structure:

```
{
  "extraData": "AAECAw==",
  "filename": "example.txt",
  "comment": "This is the comment"
}
```

- **filename** – the original filename embedded in the Gzip data (if present)
- **comment** – an optional descriptive comment (if present)
- **extraData** – optional additional binary data, returned as a Base64-encoded string

Any of these fields may be omitted if they were not included when the Gzip data was created.

Returns true for success, false for failure.

### Gzip.IsGzip

`Chilkat 11.7.0 · js · Gzip · IsGzip · method · since 11.0.0`

```javascript
var boolVal = IsGzip(bd);
```

· return: `boolean`  
· bd: `CkBinData`

Checks whether the data contained in a `BinData` object is in Gzip format.

Returns `true` if the data is Gzip-formatted, or `false` otherwise.

### Gzip.SetDt

`Chilkat 11.7.0 · js · Gzip · SetDt · method`

```javascript
var success = SetDt(dt);
```

· return: `boolean`; `true` for success, `false` for failure  
· dt: `CkDateTime`

Sets the last-modified date/time to embed in the Gzip file when a `Compress*` method is called.

If no date/time is explicitly set, the current system date/time is used.

Returns true for success, false for failure.

### Gzip.SetExtraData

`Chilkat 11.7.0 · js · Gzip · SetExtraData · method · since 11.0.0`

```javascript
var success = SetExtraData(encodedData, encoding);
```

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

· return: `boolean`; `true` for success, `false` for failure  
· encodedData: `string`  
· encoding: `string`

Sets optional extra binary data to include in the Gzip header when a `Compress*` method is called.

The data is passed as an encoded string. Supported encodings include `base64`, `hex`, `ascii`, and many others.

Returns true for success, false for failure.

### Gzip.UncompressBd

`Chilkat 11.7.0 · js · Gzip · UncompressBd · method · since 9.5.0.67`

```javascript
var success = UncompressBd(binDat);
```

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

Decompresses Gzip data contained in a `BinData` object in place, replacing the compressed data with the uncompressed data.

Returns true for success, false for failure.

### Gzip.UncompressBdToFile

`Chilkat 11.7.0 · js · Gzip · UncompressBdToFile · method · since 11.0.0`

```javascript
var success = UncompressBdToFile(bd, filePath);
```

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

Decompresses Gzip data stored in a `BinData` object and writes the result to a file.

Returns true for success, false for failure.

### Gzip.UncompressFile

`Chilkat 11.7.0 · js · Gzip · UncompressFile · method`

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

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

Decompresses a Gzip file and writes the result to the specified output path.

The output filename is provided by the caller. The filename embedded in the Gzip data is not used.

Returns true for success, false for failure.

### Gzip.UncompressFileToString

`Chilkat 11.7.0 · js · Gzip · UncompressFileToString · method`

```javascript
var strVal = UncompressFileToString(srcPath, charset);
```

**Full documentation for this method (same in every language):** [List of Valid Charsets](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/charsets_supported_by_chilkat.md)

· return: `string`  
· srcPath: `string`  
· charset: `string`

Decompresses a Gzip file that contains text and returns the uncompressed text as a string.

The `charset` parameter specifies the character encoding of the uncompressed text, such as `utf-8`, `iso-8859-1`, `windows-1252`, `shift_JIS`, `big5`, etc.

Returns `null` on failure

### Gzip.UncompressStringENC

`Chilkat 11.7.0 · js · Gzip · UncompressStringENC · method`

```javascript
var strVal = UncompressStringENC(inStr, charset, encoding);
```

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

· return: `string`  
· inStr: `string`  
· charset: `string`  
· encoding: `string`

Decompresses Gzip data provided as an encoded string and returns the uncompressed result as text.

The input string is first decoded using the specified encoding, such as `base64`, `hex`, `url`, `base32`, quoted-printable, etc. The decoded Gzip data is then decompressed and converted to text using the specified character set.

Returns `null` on failure

### Gzip.UnTarGz

`Chilkat 11.7.0 · js · Gzip · UnTarGz · method`

```javascript
var success = UnTarGz(gzPath, destDir, bNoAbsolute);
```

· return: `boolean`; `true` for success, `false` for failure  
· gzPath: `string`  
· destDir: `string`  
· bNoAbsolute: `boolean`

Extracts a `.tar.gz` archive to a directory.

The Gzip decompression and TAR extraction are performed in streaming mode. No temporary files are created, and memory usage remains small and constant.

If `bNoAbsolute` is `true`, absolute paths in the TAR archive are not allowed. This helps protect against extracting files to unsafe locations, such as system directories.

Returns true for success, false for failure.

### Gzip.XfdlToXml

`Chilkat 11.7.0 · js · Gzip · XfdlToXml · method`

```javascript
var strVal = XfdlToXml(xfldData);
```

**Full documentation for this method (same in every language):** [More about XFDL](https://www.chilkatsoft.com/ai-docs/v/11.7.0/articles/xfdl.md)

· return: `string`  
· xfldData: `string`

Converts encoded and compressed XFDL data to a decompressed XML string.

XFDL data is often stored in an ASCII-safe compressed form, such as `asci-gzip` or `asc-gzip`. Despite the name, this does not always mean the data is a standard `.gz` file. In some XFDL files, the compressed payload uses the raw deflate format rather than the full Gzip file format.

Chilkat automatically detects the actual encoding and compression format used by the XFDL data. It decodes the ASCII/Base64 representation, determines whether the compressed data is Gzip or deflate, decompresses it correctly, and returns the resulting XML string.

This allows applications to call `XfdlToXml` without needing to manually distinguish between XFDL variants such as Base64+Gzip and Base64+Deflate.

Returns the decoded and decompressed XML string.

**XFDL (Extensible Forms Description Language)** is an XML-based format used to define secure, interactive electronic forms—often including digital signatures and integrity protections—commonly used in government and enterprise applications.

Returns `null` on 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), [`CkDateTime`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/js/classes/CkDateTime.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)