(JavaScript) Compressing StringBuilder Data Using CompressSb (Single Call and Chunked)

See more Compression Examples

1. Single-call compression, where the entire input is compressed in one operation.
2. Chunked compression, where the input is split into multiple parts and processed sequentially using the FirstChunk and LastChunk properties.

The example shows how compressed output is appended to a BinData object, and how the result can be verified by decompressing back to the original text. This is useful for both simple use cases and scenarios where data is processed incrementally (such as streaming or large inputs).

Key Points

• CompressSb converts text to bytes using the Charset property (UTF-8 recommended).
• Compressed data is appended to a BinData object.
• When both FirstChunk and LastChunk are true, compression is done in a single call.
• For chunked processing:
  • First chunk → FirstChunk = true, LastChunk = false
  • Middle chunks → both false
  • Final chunk → LastChunk = true
• Chunked compression is useful when processing data incrementally.

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();
compress.Algorithm = "zlib";

// ================================================================
// 1) Single-call compression (entire data in one call)
// ================================================================

var sb = new CkStringBuilder();
sb.Append("The quick brown fox jumps over the lazy dog. ");
sb.Append("This is a simple example using CompressSb.");

var bdCompressed = new CkBinData();

// When both FirstChunk and LastChunk are true (the defaults),
// the entire compression happens in a single call.
compress.FirstChunk = true;
compress.LastChunk = true;

success = compress.CompressSb(sb,bdCompressed);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

var compressedBase64 = bdCompressed.GetEncoded("base64");

console.log("Single-call compressed (base64):");
console.log(compressedBase64);

// ================================================================
// 2) Chunked compression using FirstChunk / LastChunk
// ================================================================

var bdChunkedOut = new CkBinData();

// First chunk
compress.FirstChunk = true;
compress.LastChunk = false;

var sbPart = new CkStringBuilder();
sbPart.Append("The quick brown fox ");

success = compress.CompressSb(sbPart,bdChunkedOut);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

// Middle chunk
compress.FirstChunk = false;
compress.LastChunk = false;

sbPart.Clear();
sbPart.Append("jumps over the lazy dog. ");

success = compress.CompressSb(sbPart,bdChunkedOut);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

// Final chunk
compress.FirstChunk = false;
compress.LastChunk = true;

sbPart.Clear();
sbPart.Append("This is a chunked CompressSb example.");

success = compress.CompressSb(sbPart,bdChunkedOut);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

var chunkedBase64 = bdChunkedOut.GetEncoded("base64");

console.log("Chunked compressed (base64):");
console.log(chunkedBase64);

// ================================================================
// 3) Decompress to verify correctness
// ================================================================

var sbDecompressed = new CkStringBuilder();

// Decompress in a single call (entire data already assembled)
compress.FirstChunk = true;
compress.LastChunk = true;

success = compress.DecompressSb(bdChunkedOut,sbDecompressed);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

console.log("Decompressed text:");
console.log(sbDecompressed.GetAsString());