ブラウザ内でバイナリを圧縮してコードやlocalStorageに埋め込む

const encoder = new TextEncoder();
const decoder = new TextDecoder();

const compress_supported = !!globalThis.DecompressionStream;

async function deflate(str: string): Promise<ArrayBuffer> {
  const buf = encoder.encode(str);
  if (compress_supported) {
    const stream = new Response(buf).body!.pipeThrough(new CompressionStream("deflate"));
    const buf2 = await new Response(stream as any).arrayBuffer();
    return buf2;
  } else {
    return buf.buffer;
  }
}

async function inflate(buffer: ArrayBuffer): Promise<string> {
  if (compress_supported) {
    const decompressedStream = new Blob([buffer]).stream().pipeThrough(new DecompressionStream("deflate"));
    const buf = await new Response(decompressedStream as any).arrayBuffer();
    return decoder.decode(buf);
  } else {
    return decoder.decode(buffer);
  }
}

const encode = async (raw: string) => {
    const buf = await deflate(raw);
    const u8 = new Uint8Array(buf.byteLength % 2 ? buf.byteLength + 1 : buf.byteLength);
    u8.set(new Uint8Array(buf));
    const u16 = new Uint16Array(u8.buffer);
    const u16str = Array.from(u16).map(s => String.fromCharCode(s))));
    return u16str.join('');
));

const decode = async (encoded: string) => {
    const u16c = Array.from(encoded).map((c) => c.charCodeAt(0));
    const u8c = new Uint8Array(new Uint16Array(u16c).buffer);
    const last = u8c.at(-1);
    try {
        return await inflate(
            last === 0 ? u8c.slice(0,-1) : u8c
        );
    } catch (err) {
        return await inflate(u8c);
    }
}

// usage

const input = `Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
`;

(async () => {
    console.time('all');
    console.time('encode');
    const encoded = await encode(input);
    console.timeEnd('encode');
    console.time('decode');
    const decoded = await decode(encoded);
    console.timeEnd('decode');
    console.timeEnd('all');
})();

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