Updated Solution to Third Problem

UpdatedThirdSolution.js

const bingeWatching = (timeElapsed, duration, action, amount) => {
  const timeStrToSeconds = (str) => {
    newArr = str.split(':').map(Number)
    return (newArr[0] * 3600) + (newArr[1] * 60) + newArr[2]
  }

  const secondsToTimeStr = (seconds) => {
    let hours = Math.floor(seconds / 3600)
      if (hours === 0) {
        hours = "00"
      }
    let minutes = (seconds % 3600) / 60
      if (minutes === 0) {
        minutes = "00"
      }
    let remainingSeconds = seconds - (hours * 3600) - (minutes * 60)
      if (remainingSeconds === 0) {
        remainingSeconds = "00"
      }
    return "" + hours + ":" + minutes + ":" + remainingSeconds
  }

  if (action === "Report Progress") {
    return timeStrToSeconds(timeElapsed) / timeStrToSeconds(duration) * 100
  } else if (action === "Rewind") {
      let newTime
      if (typeof amount === "string") {
        newTime = timeStrToSeconds(timeElapsed) - timeStrToSeconds(amount)
      } else if (typeof amount === "number") {
        newTime = timeStrToSeconds(timeElapsed) * (amount / 100) 
      }
      return newTime < 0 ? "00:00:00" : secondsToTimeStr(newTime)
  } else if (action === "Fast Forward") {
    let newTime
    if (typeof amount === "string") {
      newTime = timeStrToSeconds(timeElapsed) + timeStrToSeconds(amount)    
    } else if (typeof amount === "number") {
      newTime = timeStrToSeconds(timeElapsed) +  (timeStrToSeconds(duration) - timeStrToSeconds(timeElapsed)) * (amount / 100) 
    }
    return newTime > timeStrToSeconds(duration) ? "Movie Finished" : secondsToTimeStr(newTime) 
  }
}