timed-local-storage.js

import {Observable, Subject} from 'rx';
import _ from 'lodash';

export default class TimedLocalStorage {
  constructor(originalLocalStorage) {
    this.inner = originalLocalStorage;
    
    this.tick = new Subject();
    this.count = 0;
    this.elapsed = 0;
    
    const toOverride = ['key', 'getItem', 'setItem', 'removeItem', 'clear'];
    _.each(toOverride, (k) => {
      let item = k;

      this[item] = (...args) => {
        let s = performance.now();
        let ret = this.inner[item](...args);
        this.tick.onNext(performance.now() - s);

        return ret;
      };
    });
    
    this.tick
      .do((elapsed) => {
        this.start = this.start || performance.now();
        this.count++;
        this.elapsed += elapsed;
      })
      .throttle(1000)
      .subscribe(() => {
        let total = performance.now() - this.start - 1000;
        if (total < 0) total += 1000;

        let percentage = this.elapsed / total * 100;
        if (total > 50) {
          
          console.log(`Local Storage accounted for ${this.elapsed}ms of ${total}ms (${percentage}%)`);
        }
        
        this.start = null;
        this.count = 0;
        this.elapsed = 0;
      });
  }
  
  get length() {
    return this.inner.length;
  }
}