cache.js

import WaveSurfer from 'wavesurfer.js'

const url = '/examples/audio/demo.wav'
const cache = localStorage.getItem('cache' + url)

const wavesurfer = WaveSurfer.create({
  container: document.body,
  waveColor: 'rgb(200, 0, 200)',
  progressColor: 'rgb(100, 0, 100)',
  url,
  peaks: cache && JSON.parse(cache),
})

wavesurfer.on('ready', () => {
  const peaks = wavesurfer.exportPeaks()
  localStorage.setItem('cache' + url, JSON.stringify(peaks))
})