old_contents: var tickWave = require('./tickWave')
  
  module.exports = function (state, dt) {
    // Parameters
    //   state
    //   dt
    //     simulation time, seconds
    //
  
    // To avoid huge wave of particles when the page gains focus after a while,
    // the particles are created only if dt is close to given framerate.
    if (dt > 0.5) {
      return
    }
  
    // Remove dead waves
    state.waves = state.waves.filter(function (wave) {
      return wave.alive
    })
  
    // Simulate each wave. Each wave has its own options.
    state.waves.forEach(function (wave) {
      tickWave(state, wave, dt)
    })
  }
  
new_contents: var tickWave = require('./tickWave')
  
  module.exports = function (state, dt) {
    // Parameters
    //   state
    //   dt
    //     simulation time, seconds
    //
  
    // To avoid huge wave of particles when the page gains focus after a while,
    // the particles are created only if dt is close to given framerate.
    if (dt > 0.5) {
      return
    }
  
    // DEBUG TOOL
    // console.log('number of waves', state.waves.length)
  
    // Remove dead waves
    state.waves = state.waves.filter(function (wave) {
      return wave.alive
    })
  
    // Simulate each wave. Each wave has its own options.
    state.waves.forEach(function (wave) {
      tickWave(state, wave, dt)
    })
  }
  
subject: Add debug tool to count waves