(JavaScript) Compress a File to Gzip with Custom Metadata

See more Gzip Examples

This example demonstrates how to use the CompressFile method to create a Gzip (.gz) file while customizing the metadata embedded in the Gzip header.

Before compression, several properties are set:

• Comment: Adds a descriptive comment to the Gzip file.
• Filename: Specifies the filename to embed in the Gzip data, which may be used by extraction tools as the default output name.
• CompressionLevel: Controls the tradeoff between compression ratio and speed (set to maximum in this example).
• LastModStr: Sets the last-modified timestamp using an RFC 822 formatted date string.

After setting these properties, the input file is compressed and written to a .gz file. This approach allows you to embed meaningful metadata along with the compressed data.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

// This example demonstrates how to compress a file to Gzip format
// while setting custom metadata such as comment, filename,
// compression level, and last-modified date.

var gzip = new CkGzip();

// Set custom Gzip properties:
gzip.Comment = "Example Gzip file created with Chilkat";
gzip.Filename = "custom_name.txt";
gzip.CompressionLevel = 9;
gzip.LastModStr = "Wed, 1 Apr 2025 12:45:26 -0500";

// The file to be compressed:
var inputFile = "example.txt";
var outputFile = "example.txt.gz";

// Compress the file:
success = gzip.CompressFile(inputFile,outputFile);
if (success == false) {
    console.log(gzip.LastErrorText);
    return;
}

console.log("Compression successful.");
console.log("Gzip file created: " + outputFile);