show canvas on image when button is clicked
  < div  class = "info" >     < p  id = "points-info" > No points yet </ p > </ div > < div  class = "output" >     < img  id = "image"  src = "https://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Image_created_with_a_mobile_phone.png/1200px-Image_created_with_a_mobile_phone.png"  width = "500"  height = "500" >     < canvas  id = "canvas"  width = "500"  height = "500" ></ canvas >     < p  id = "coordinates" ></ p > </ div > < button  id = "show-canvas-btn" > Show Canvas </ button > < style > canvas  {     width : 500px ;     height : 500px ;     display : none ;     border : 3px  solid  #333 ;     background-size : cover ;     cursor : crosshair ; } </ style > < script > var  canvas  = document . getElementById ( 'canvas' ); var  ctx  = canvas . getContext (...