Web Animation, how to animate the background rgba color

Question

I want to animate the background color in rgba for a modal so it fades in. I cant use opacity as the div inside the modal I dont want to be transparent. I cant use Jquery but I am using React.

I'm not getting an error by the below does not work

const modal = document.getElementById('modal');
modal.animate(
[
  {backgroundColor: 'rgba(255, 0, 0, 0)'}, 
  {backgroundColor: 'rgba(255, 0, 0, 0.8)'}
], 
  {duration: 200, easing: 'ease-in-out', fill: 'forwards'}
);

Answer 1

Use setInterval function to change color in javascript.

var change=0;
var colorEvent= setInterval("changeColor();", 50);
function changeColor(){
  if(change<100){           
      document.getElementById("modal").style.backgroundColor="rgb(255,0,"+change+")";
  }
  else 
    clearInterval(colorEvent);
  change+=1;
  console.log(change);
}

#modal{
    height:50px;
    background-color:rgb(255,0,0);
}

<div id="modal"></div>

or changing opacity

var change=0.0;
if(change<0.8){
  setInterval(function(){
      document.getElementById("modal").style.backgroundColor="rgb(255,0,0,"+change+")";
      change+=0.01;
  }, 10);
}

#modal{
    height:50px;
    background-color:rgb(255,0,0,0);
}

<div id="modal"></div>