Web Storage (localStorage, sessionStorage, cookies)

What data optimization technique is implemented in this storage code?
const storage = {
  compress(data) {
    return btoa(JSON.stringify(data));
  },
  
  decompress(data) {
    return JSON.parse(atob(data));
  },
  
  set(key, value) {
    try {
      const compressed = this.compress(value);
      localStorage.setItem(key, compressed);
      return true;
    } catch (e) {
      return false;
    }
  },
  
  get(key) {
    const data = localStorage.getItem(key);
    return data ? this.decompress(data) : null;
  }
};
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