My own function fadeIn on Vanilla.js

fadeIn

function fadeIn(selector, time){

	let timer = time || 400;
	let element = document.querySelectorAll(selector)[0];
	let timeForSetInterver = 20;
	let opacityEnd = 1;
	let count = timer / timeForSetInterver;
	let step = opacityEnd / count;
	let i = 0;

	let forClear = setInterval(function(){

		let opacity = getComputedStyle(element).opacity;

		element.style.opacity = parseFloat(opacity) + parseFloat(step);

		i++;

		if(i == count){
		clearInterval(forClear);
		element.style.opacity = 1
	}

	}, timeForSetInterver)

}