JS function for animation without CSS. Code example

function fadeIn(element, time) {
		let opacity = 0;
		const interval = 16;
		const duration = time;
	  
		function animate() {
		  opacity += interval / duration;
		  if (opacity >= 1) {
			opacity = 1;
			clearInterval(fadeInterval);
		  }
		  element.style.opacity = opacity;
		}
	  
		const fadeInterval = setInterval(animate, interval);
}

Add function to your element:

fadeIn(element, 1000);