//html
<div id="button"></div>
<div id="video" style="display:none;>
<video width="200" height="150" controls>
<source src="vid.mp4" type="video/mp4">
</div>
//javascript
document.getElementById('button').addEventListner('click', function(){
let video = document.getElementById('video');
function showVideo(){
video.style.display = "block";
}
function hideVideo(){
video.style.display = "none"
}
showVideo();
hideVideo();
}