storage.js

class Storage {
  constructor(engine) {
    this.engine = engine 
  }
  
  get totalDownloads() {
    return Number(this.engine.getItem('totalDownloads')) 
  }
  set totalDownloads(n) {
    this.engine.setItem('totalDownloads', n) 
  }
  
  get files() {
    const fs = []
    for (let i = 0; i < this.engine.length; i++) {
      const k = this.engine.key(i)
      if (isFile(k)) {
        fs.push(JSON.parse(this.engine.getItem(k))) // parse or whatever else
      }
    }
    return fs
  }
  
  addFile(file) {
    // something something engine.setItem(...) 
  }
  
  // etc
}