A benchmark to see how many items can be stored using WebCompressor

local-storage-vs-compression.js

const findLimit = async (type, create) => {
  console.log(
    `%c ${type} benchmark `,
    `font-weight:bold;color:white;background-color:black`
  );
  localStorage.clear();
  let i = 0;
  let length = 0;
  while (true) {
    try {
      if (i < 1)
        console.time(`${type} storing time`);
      const value = (await create()).toString();
      localStorage.setItem(i, value);
      if (i++ < 1)
        console.timeEnd(`${type} storing time`);
      length += value.length;
    }
    catch (limit) {
      console.log(
        `%c${type}`,
        `font-weight:bold`,
        `stored ${i} items with overall length of ${length}`
      );
      break;
    }
  }
}

const value = () => String(Math.random() + new Date).repeat(1024);

import('https://unpkg.com/web-compressor?module').then(
  async ({default: WebCompressor}) => {
    await findLimit('plain', value);

    const b64deflate = new WebCompressor().compress;
    await findLimit('base64 + deflate', () => b64deflate(value()));

    const b64gzip = new WebCompressor('gzip').compress;
    await findLimit('base64 + gzip', () => b64gzip(value()));

    const utf16deflate = new WebCompressor('deflate', 'utf-16').compress;
    await findLimit('utf-16 + deflate', () => utf16deflate(value()));

    const utf16gzip = new WebCompressor('gzip', 'utf-16').compress;
    await findLimit('utf-16 + gzip', () => utf16gzip(value()));
  }
);

Validation Test

const value = () => String(Math.random() + new Date).repeat(1024);

import('https://unpkg.com/web-compressor?module').then(
  async ({default: WebCompressor}) => {
    const {compress, decompress} = new WebCompressor('deflate', 'utf-16');
    localStorage.clear();
    const entry = value();
    console.time('validation test');
    localStorage.setItem('test', await compress(entry));
    console.assert(
      await decompress(localStorage.getItem('test')) === entry,
      'unexpected entry'
    );
    console.timeEnd('validation test');
  }
);

Results

plain benchmark

plain storing time: 1.3828125ms
plain stored 60 items with overall length of 5166080

base64 + deflate benchmark

base64 + deflate storing time: 10.251953125ms
base64 + deflate stored 9706 items with overall length of 5205052

base64 + gzip benchmark

base64 + gzip storing time: 8.6259765625ms
base64 + gzip stored 9431 items with overall length of 5206148

utf-16 + deflate benchmark

utf-16 + deflate storing time: 6.224853515625ms
utf-16 + deflate stored 25385 items with overall length of 5126905

utf-16 + gzip benchmark

utf-16 + gzip storing time: 14.4921875ms
utf-16 + gzip stored 24668 items with overall length of 513063