如何利用css的延迟属性结合简单js实现渐变动效

通过简单的SCSS+TypeScript。我们可以实现视频中常见的渐变动效，这里是通过原生CSS+JS来实现的，下图为动效中效果截图：

html部分，用来定义文字基本结构

<div class="reveal">WWW.ZHUIGE.COM</div>

CSS部分，主要通过伪类和关键帧动画来控制控制字符的透明度，位移，缩放来实现动画

@import url("https://fonts.googleapis.com/css?family=Raleway:400,400i,700");

body {
  display: flex;
  height: 100vh;
  justify-content: center;
  align-items: center;
  text-align: center;
  background: #f0f1f0;
}

.reveal {
  position: relative;
  display: flex;
  color: #1173EB;
  font-size: 2em;
  font-family: Raleway, sans-serif;
  letter-spacing: 3px;
  text-transform: uppercase;
  white-space: pre;

  span {
    opacity: 0;
    transform: scale(0);
    animation: fadeIn 2.4s forwards;
  }

  &::before,
  &::after {
    position: absolute;
    content: "";
    top: 0;
    bottom: 0;
    width: 2px;
    height: 100%;
    background: #1173EB;
    opacity: 0;
    transform: scale(0);
  }

  &::before {
    left: 50%;
    animation: slideLeft 1.5s cubic-bezier(0.7, -0.6, 0.3, 1.5) forwards;
  }

  &::after {
    right: 50%;
    animation: slideRight 1.5s cubic-bezier(0.7, -0.6, 0.3, 1.5) forwards;
  }
}

@keyframes fadeIn {
  to {
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes slideLeft {
  to {
    left: -6%;
    opacity: 1;
    transform: scale(0.9);
  }
}

@keyframes slideRight {
  to {
    right: -6%;
    opacity: 1;
    transform: scale(0.9);
  }
}

js部分，主要控制延迟

let duration = 0.8;
let delay = 0.3;
let revealText = document.querySelector(".reveal");
let letters = revealText.textContent.split("");
revealText.textContent = "";
let middle = letters.filter(e => e !== " ").length / 2;
letters.forEach((letter, i) => {
  let span = document.createElement("span");
  span.textContent = letter;
  span.style.animationDelay = `${delay + Math.abs(i - middle) * 0.1}s`;
  revealText.append(span);
});