JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">

     <video muted id="video" src="http://s3-eu-west-1.amazonaws.com/advertisingcdn/overslide-creatives/dads-army/Dads_Army.mp4" controls>
            </video>
        </div>

JavaScript

var myPlayer = document.querySelector('#video');
    var percentageCompleted = 0;
    var totalLength = 0;
    var videoStarted, videoTwentyFive, videoFifty, videoSeventyFive, videoComplete = false;

myPlayer.on('timeupdate', getPercentage);
  
    function getPercentage(){

          percentageCompleted = (myPlayer.currentTime()/totalLength)*100;
          //console.log('percentage', (percentageCompleted+'%'));
  
          // is 0
          if((!videoStarted) && (percentageCompleted>0))
          {
            console.log('VIDEO_STARTED');
            videoStarted=true;
            
            window.dataLayer = window.dataLayer || [];
            window.dataLayer.push({
              'event': 'playStart'
            });
          }
          // is 25
          if((!videoTwentyFive) && (percentageCompleted>25))
          {
            console.log('VIDEO_25');
            videoTwentyFive=true;
           
            window.dataLayer = window.dataLayer || [];
            window.dataLayer.push({
              'event': 'playTwentyFive'
            });
          }
          // is 50
          if((!videoFifty) && (percentageCompleted>50))
          {
            console.log('VIDEO_50');
            videoFifty=true;
            
            window.dataLayer = window.dataLayer || [];
            window.dataLayer.push({
              'event': 'playFifty'
            });
          }
          // is 75
          if((!videoSeventyFive) && (percentageCompleted>75))
          {
            console.log('VIDEO_75');
            videoSeventyFive=true;
            
            window.dataLayer = window.dataLayer || [];
            window.dataLayer.push({
              'event': 'playSeventyFive'
            });
          }
          // is 100
          if((!videoComplete) && (percentageCompleted>99))
          {
            console.log('VIDEO_100');
            videoComplete=true;
            
            window.dataLayer = window.dataLayer || [];
           ...