(JavaScript) Compressing and Decompressing Files Using Streaming (CompressFile / DecompressFile)

See more Compression Examples

This example demonstrates how to compress a file to a binary format and then restore it using the Chilkat.Compression class. The CompressFile method reads the source file, compresses it using the specified algorithm, and writes the result to a destination file. The DecompressFile method performs the reverse operation, restoring the original file from the compressed data.

Both operations are performed internally in streaming mode, allowing files of any size to be processed efficiently without loading the entire file into memory. The example also includes a simple verification step by comparing file sizes to confirm that the decompressed output matches the original input.

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 assumes the Chilkat API has already been unlocked.
// See Global Unlock Sample for sample code.

var compress = new CkCompression();

// Use the zlib algorithm (recommended for general use)
compress.Algorithm = "zlib";

// ------------------------------------------------------------------
// Compress a file
// ------------------------------------------------------------------

var inputFile = "c:/temp/example.txt";
var compressedFile = "c:/temp/example.txt.zlib";

success = compress.CompressFile(inputFile,compressedFile);
if (success == false) {
    console.log("Compression failed:");
    console.log(compress.LastErrorText);
    return;
}

console.log("File compressed successfully:");
console.log("  Input:      " + inputFile);
console.log("  Compressed: " + compressedFile);

// ------------------------------------------------------------------
// Decompress the file back to its original form
// ------------------------------------------------------------------

var decompressedFile = "c:/temp/example_restored.txt";

success = compress.DecompressFile(compressedFile,decompressedFile);
if (success == false) {
    console.log("Decompression failed:");
    console.log(compress.LastErrorText);
    return;
}

console.log("File decompressed successfully:");
console.log("  Output: " + decompressedFile);

// ------------------------------------------------------------------
// Optional: Verify file sizes (basic sanity check)
// ------------------------------------------------------------------

var fac = new CkFileAccess();

var originalSize = fac.FileSize(inputFile);
var restoredSize = fac.FileSize(decompressedFile);

console.log("Original file size:   " + originalSize);
console.log("Restored file size:   " + restoredSize);

if (originalSize == restoredSize) {
    console.log("Sizes match (basic verification successful).");
}
else {
    console.log("Warning: File sizes differ.");
}