old_contents: import LRU from 'lru-cache'
  import path from 'path'
  import fs from 'fs-plus'
  import _ from 'underscore'
  
  export default class ReadCache {
    constructor (folder, cacheSize) {
      this.path = path.join(folder, 'Storage', 'db.json')
      this.cache = LRU({
        max: cacheSize,
        length: function (n) {
          return n.length
        }
      })
    }
  
    load () {
      var result = {}
      try {
        result = JSON.parse(fs.readFileSync(this.path, 'utf8'))
      } catch (e) {
        console.log(e)
      }
  
      if (result['read']) {
        _.each(result['read'].reverse(), function (val) {
          this.set(val)
        }, this)
      }
    }
  
    store () {
      var result = []
      this.cache.forEach(function (value, key) {
        result.push(key)
      })
      fs.writeFileSync(this.path, JSON.stringify({ read: result }), 'utf8')
    }
  
    set (val) {
      val = val.toString()
      return this.cache.set(val, val)
    }
  
    contains (val) {
      val = val.toString()
      return this.cache.has(val)
    }
  }
  
new_contents: import LRU from 'lru-cache'
  import path from 'path'
  import fs from 'fs-plus'
  import _ from 'underscore'
  
  export default class ReadCache {
    constructor (folder, cacheSize) {
      this.path = path.join(folder, 'Storage', 'db.json')
      this.cache = LRU({
        max: cacheSize
      })
    }
  
    load () {
      var result = {}
      try {
        result = JSON.parse(fs.readFileSync(this.path, 'utf8'))
      } catch (e) {
        console.log(e)
      }
  
      if (result['read']) {
        _.each(result['read'].reverse(), function (val) {
          this.set(val)
        }, this)
      }
    }
  
    store () {
      var result = []
      this.cache.forEach(function (value, key) {
        result.push(key)
      })
      fs.writeFileSync(this.path, JSON.stringify({ read: result }), 'utf8')
    }
  
    set (val) {
      return this.cache.set(val, val)
    }
  
    contains (val) {
      return this.cache.has(val)
    }
  }
  
subject: Use integer for cache key