使用新的 CSS 函数优化 CSS 基于时间的动画-css教程-PHP中文网

作者：Emmanuel Odioko✏️

长期以来，对数学函数的有限支持使得创建基于时间的 CSS 动画变得更具挑战性。传统动画依赖于关键帧和持续时间，缺乏基于复杂计算的基于时间的更新的灵活性。随着 mod()、round() 和三角函数等 CSS 函数的引入，开发人员现在可以探索如何掌握 CSS 中基于时间的动画。

开始之前需要了解的事情

要充分利用这篇关于使用新 CSS 函数在 CSS 中实现基于时间的动画的内容，您应该对 CSS 动画和过渡有很好的了解。您应该能够知道如何使用@keyframes 创建动画并控制它们的时间。您还应该对 JavaScript 有基本的了解，更多地关注操作 DOM 元素和响应用户事件的能力。

最后，了解新的 CSS 函数（如 calc()），并准备好探索新兴功能（如 mod()）、三角函数（包括 sin() 和 cos() 以及 round()）将打下良好的基础。

读完本文后，您将了解传统上如何使用 JavaScript 在 HTML 画布上实现动画，以及它们与较新的 CSS 函数的比较。我们将了解使用 mod()、round() 和三角函数相对于传统 CSS 关键帧的易用性。

Optimizing CSS time-based animations with new CSS functions

什么是 CSS 基于时间的动画？

基于时间的动画并不新鲜——它们已经存在十多年了。有些使用起来很复杂，而另一些则不然。您知道那些以数学计算为主的 CSS 文件吗？基于时间的动画就是其中的一部分。

顾名思义，这些动画与时间密切相关，元素的属性，如位置、大小、颜色、不透明度等，都会随着时间而变化。 CSS 基于时间的动画可产生平滑的过渡，增强 Web 应用程序的感觉并提供更好的用户体验。

基于时间的 CSS 动画主要由定义的开始和结束时间轴以及插值点组成。这里的插值是指随着动画的进行，在给定的持续时间内计算动画开始和结束之间的中间值。插值的原因是为了提供从初始状态到最终状态的平滑过渡。

基于时间的动画是通过 CSS 变量和一些数学函数的组合来实现的。这种统一性使开发人员能够创建随时间变化的动画，并产生关键帧动画只能梦想的更灵活的动画。让我们来分解一下关键概念及其工作原理。

分解基于时间的动画

在本节中，我们将把创建基于时间的动画的一般结构分解为关键组件。

初始状态

初始状态定义了动画开始之前元素的起始属性。这可以是指定的位置、大小、颜色、不透明度等。示例如下：

.box {
  opacity: 0;
  transform: translateY(-20px);
}

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在上面的代码中，我们有一个带有类 box 的元素的初始状态，它定义了它的不透明度和变换属性。

动画触发器指定启动动画的事件。常见触发器包括用户交互（例如单击或悬停）、页面加载事件或应用程序中的特定条件（例如用户完成操作）。

动画的属性包括动画时长、定时函数、延迟、迭代次数、方向和填充模式。动画可能具有部分或全部这些属性。下面显示了带有悬停选择器的触发器示例：

.box:hover {
  animation: fadeIn 1s ease-in-out forwards;
}

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这显示了添加的动画 fadeIn，当带有类框的元素悬停并持续一秒钟时会触发该动画。还指定了动画行为和时间。阅读本文以获取有关动画和过渡计时函数的更多信息。

插补点

如前所述，这些是动画在时间轴上各个点的中间状态。每个关键帧指定元素在特定时刻的属性，允许初始状态和最终状态之间的逐渐过渡。插值点的一个示例实现是 CSS keyframes 属性：

@keyframes fadeIn {
  0% {
    opacity: 0;
    transform: translateY(-20px);
  }
  100% {
    opacity: 1;
    transform: translateY(0);
  }
}

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上面的示例使用关键帧来定义动画进度的 0% 和 100% 处的 fadeIn 动画的属性。

Common uses of time-based animations

Time-based animation has become increasingly essential in web applications as it helps with better user experience. The usage of these animations ranges from subtle micro-interactions to significant site transitions, giving web apps a more dynamic feel. Below are common use cases of these animations.

Micro-interactions

Micro-interactions are small, often subtle, and reusable animations that occur in response to user actions. These brief animations provide feedback. You may have come across animations such as pop-up warnings, loading spinners indicating ongoing processes, or a button indicating a click action. All of these are micro-interactions and consist of time-based animations. Optimizing CSS time-based animations with new CSS functions Image source: https://userpilot.com/blog/micro-interaction-examples/[/caption]

In the image above, we have a submit button which shows a loader and a tick when the user clicks on it. The essence of these micro interactions is to commit to the user the process of the submission and the success of the operation.

Transitions

Site transitions are used to indicate state or page changes on a web application to create a fluid user experience using effects such as fading, sliding, or scaling elements. With time-based animations, these transitions are possible. Common transition effect applications are toggling navigation and side menus, parallax animations, opening and closing of modals, etc.

Image source: https://medium.com/@9cv9official/create-a-beautiful-hover-triggered-expandable-sidebar-with-simple-html-css-and-javascript-9f5f80a908d1[/caption] Image source: https://medium.com/@9cv9official/create-a-beautiful-hover-triggered-expandable-sidebar-with-simple-html-css-and-javascript-9f5f80a908d1

In the GIF above, there is a sidebar which uses a transition animation to expand the sidebar on a mouse hover event.

Exploring new CSS functions

Let’s get into the new mathematical CSS functions mod(), round(), and the trigonometric functions sin(), cos() and tan() while discussing each in detail.

Mod () function

Like the JavaScript modulo operator %, this function returns the remainder after an arithmetic modulus operation has been carried out on two operands. In essence, the modulus is the leftover value after the dividend is divided by the other operand, the divisor, and no more division can occur. In JavaScript, using the modulo operator will take the following form:10%4.

This operation would leave behind a Modulus of 2 as 10 is only divisible by the divisor 4 twice, leaving behind a remainder of 2. Similarly, the CSS Mod function would perform the same function with the following syntax instead: mod(10, 4).

It is also important to note that the modulus takes the sign of the divisor. As such, the result of mod(10, -4) would be -2 instead.

Mod() parameters and syntax

The mod() function primarily accepts two sets of parameters mod(dividend, divisor) which are essentially two comma-separated values. These operands must be of the same dimension for them to be valid and can take a variety of values as parameters thereby improving the range of its application. Operands passed to mod() can be numbers, percentages, or dimensions.

Mod() can also take in the unit of its operands (e.g. px, rem, vh, deg) and can also handle mathematical calculations as dividend or divisor. Below are some examples showing the use of this CSS function:

/* using <numbers> without units */
scale: mod(18, 7); /* result is 4 */

/* <percentage> and <dimension>  with units  */
height: mod(100vh, 30vh); /* result is 10vh */
width: mod(500px, 200px); /* result is 100px */
transform: rotate(mod(90deg, 20deg)); /* result is 10deg */

/* negative <percentage> and <dimension>  with units  */
height: mod(18rem, -4rem); /* result is 2rem */
rotate: mod (180deg, -100deg); /* result is 80deg */

/* working with calculations */
width: mod(40px*2, 15px); /* result is 5px */
transform: scale(mod(2*3, 1.8)); /* result is 0.6 */  
rotate: mod(10turn, 8turn/2); /* result is 2turn */

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The code block above shows different applications of the mod() in CSS styles.

While the examples shown use known values, time-based functions are expected to be used with CSS variables which are dynamic and make it possible for the styles to change values depending on the variable passed to the function. The outcome of the operation is then dependent on the calculation using the specified variables, and can produce a wider range of outcomes compared to when hardcoded values are used.

Below you’ll find the general syntax for all possibilities of mod() as illustrated by MDN:

<mod()> = 
  mod( <calc-sum> , <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

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In the syntax above, calc-sum represents the operands of the modulus operation. The syntax also shows the types of values calc-sum can contain and the possibility of negative and positive values. Furthermore, the syntax above also shows the possible calc-keywords e, pi, infinity, -infinity, and NaN.

round() function

The CSS round() function value is based on a specified rounding strategy. Note that strategy refers to the pattern of rounding the value such as rounding up or down, rounding to zero, rounding to the nearest occurrence of a number, etc..

round() parameters and syntax

The syntax for applying the CSS round() is given below:

round(<rounding-strategy>, valueToRound, roundingInterval)

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Here's a breakdown of the CSS round() function into smaller bits and highlights of the functions of each keyword and the possible values they can take.

rounding-strategy

The rounding strategy is the type of technique that would be used to round a specified value. This is optional (defaults to nearest if unspecified), and can be one of the following:

up — rounds value up to the nearest integer multiple of the specified roundingInterval. This operation is similar to JavaScript’s Math.ceil() method and will produce a more positive result if the value is negative
down — rounds valueToRound down to the nearest integer multiple of the specified roundingInterval. This is similar to JavaScript’s Math.floor() method and will produce a more negative result if the value is negative
nearest — rounds the valueToRound to the nearest integer multiple of roundingInterval. The result obtained may be higher or lower than the value, depending on how close it is to a multiple of the roundingInterval
to-zero — rounds the value to the nearest integer multiple of roundingInterval closer to/towards zero and is equivalent to JavaScript’s trunc() method

valueToRound

This is the value we intend to round using the function, and it can be a , , , or even mathematical expressions like we had in the mod() function.

roundingInterval

The rounding interval refers to the interval a value is rounded with a reference to. This entry can be a , , ,or a mathematical expression.

Below is an example illustrating the use of the CSS round() function:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body{
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      margin: 0;
    }

    /* using the round() function */
    .ball {
      width: 100px;
      height: 100px;
      background-color: red;
      color: white;
      text-align: center;
      line-height: 100px;
      margin: 10px;
    }
    .ball-1{
        border-radius: round(down, 70%, var(--rounding-interval)); /*rounded down to the interval of 50% */
    }

    .ball-2{
        border-radius: round(up, 70%, var(--rounding-interval2)); /* rounded up to interval of 100% */
    }

    .ball-3{
        border-radius: round(nearest, 15%, var(--rounding-interval3)); /* rounded to the nearest interval 25% */
    }

  </style>
</head>
<body>
    <!-- rounded containers -->
  <div class="ball ball-1" style="--rounding-interval:50%;">rounded 50%</div>
  <div class="ball ball-2" style="--rounding-interval2:100%;"> rounded 100%</div>
  <div class="ball ball-3" style="--rounding-interval3:25%;"> rounded 25%</div>
</body>
</html>

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In this example, we used round() and CSS variables to round values to a specified roundingInterval in the style of each element. Below is the outcome of this example: Optimizing CSS time-based animations with new CSS functions The formal syntax of the CSS round() function according to MDN docs is given by the following:

<round()> = 
  round( <rounding-strategy>? , <calc-sum> , <calc-sum>? )  

<rounding-strategy> = 
  nearest  |
  up       |
  down     |
  to-zero  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

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In the syntax above, rounding-strategy is the intended rounding pattern and calc-sum represents the operands. The formula also shows the possible entries for rounding-strategy and calc-sum. Finally, it outlines the possible calc-keywords e, pi, infinity, -infinity, and NaN.

Trigonometric functions

The CSS trigonometric functions perform the same operations as in mathematics, as such, the sin() function returns the sine of a number as a value between the range of -1 and 1, cos() returns the cosine of a value, and tan() returns the tangent of a specified value.

Arguments passed to these functions must be either a number or an angle, and they will be treated as radians. Units such as deg and turn represent angle and can be used with arguments here.

Example applications of these functions are shown below:

scale: sin(45deg); /* result is 0.7071067811865475 */
rotate: cos(30deg); /* result is 0.8660254037844387 */
height: calc(50px * tan(30deg)); /* result is 28.86751345948129px */

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All trigonometric CSS functions bear similarity, taking in only a single parameter that is resolved to an angle.

Parameters and syntax of sin()

Sin() takes in only one parameter which must be a number or angle, or a mathematical expression that resolves to either of them. The syntax of sin() is as follows: \

sin(angle)

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The formal syntax of sin() is shown below: \

<sin()> = 
  sin( <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

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The syntax above shows the possible values for calc-sum and calc-keyword.

Parameters and syntax of cos()

The parameter of cos() is either a number, an angle, or contains a single calculation that must resolve to either type.

As such, the syntax for cos() is the following:

cos(angle)

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The formal syntax of all possibilities of cos() is below:

<cos()> = 
  cos( <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

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Where calc-sum is the parameter, calc-value is the allowed types of parameters, and calc-keywords are possible units that can be added to the mathematical expression.

Parameters and syntax of tan()

The tan() function also takes a number, an angle, or a single calculation that must resolve to either type, similar to the other trigonometric functions. The syntax of tan() is given by the following:

tan(angle)

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The formal syntax of this function is shown below:

<tan()> = 
  tan( <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

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This syntax shows all possible values of calc-sum, the operand, and the calc-keyword.

Comparing timing animations between CSS functions and keyframes

In this section, we will create an animation using CSS functions, keyframes for an alternative, and JavaScript for a second alternative. In the end, we will compare the code and contrast the approaches to determine the benefits of usingCSS functions in creating CSS animations over other options.

Creating animation with CSS functions

Let's start by creating our music beat bar animation using CSS functions. This animation focuses on animating multiple bars, changing the property of the height and background colors using values generated with CSS functions:

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Beats Bar Animation with CSS Functions</title>
  <style>
    :root {
      /* change the value of --t infinitely */
      animation: animate-time 1000ms linear infinite;
    }

    @keyframes animate-time {
      from {
        --t: 0;
      }

      to {
        --t: 100000;
      }
    }

    body {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      background-color: #222;
      margin: 0;
    }

    .container {
      height: 500px;
      width: 250px;
      position: relative;
      display: flex;
      gap: 10px;
    }

    .bar {
      position: absolute;
      bottom: 0;
      width: 20px;
      height: 20px;
      --frequency: 1;
      --time: calc(var(--t) / 1000 / var(--frequency));
      --rounded-time: round(nearest, var(--time));
      /* Adjust frequency of animation */
      --amplitude: 30px;
      /* base height */
      --base-height: 20px;
      /* Transition for smooth height change */
      transition: height 0.5s ease-in-out, background 1s ease-in-out;             
      /* Calculate dynamic hue using mod and round */
      --hue: mod(round(nearest, calc(var(--time) * 10)), 360);
      --alpha: calc(0.5 + 0.5 * cos(calc(var(--time) * 1turn)));
      /* Apply dynamic linear gradient background */
      background: linear-gradient(to top,
          hsla(var(--hue), 100%, 50%, var(--alpha)),
          hsla(calc(var(--hue) + 180), 100%, 50%, var(--alpha)));
    }

    .bar1 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-a));
      margin-left: 10px;
    }

    .bar2 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-b));
      margin-left: 30px;
    }

    .bar3 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-c));
      margin-left: 50px;
    }

    .bar4 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-d));
      margin-left: 70px;
    }

    .bar5 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-e));
      margin-left: 90px;
    }

    .bar6 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-f));
      margin-left: 110px;
    }

    .bar7 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-g));
      margin-left: 130px;
    }

    .bar8 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-h));
      margin-left: 150px;
    }

    .bar9 {
      /* Calculate height based on rounded time */
      height: calc(var(--base-height) + var(--amplitude) * var(--rounded-time)/46 * var(--index-i));
      margin-left: 170px;
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="bar bar1" style="--index-a: 1;"></div>
    <div class="bar bar2" style="--index-b: 2;"></div>
    <div class="bar bar3" style="--index-c: 4;"></div>
    <div class="bar bar4" style="--index-d: 6;"></div>
    <div class="bar bar5" style="--index-e: 8;"></div>
    <div class="bar bar6" style="--index-f: 6;"></div>
    <div class="bar bar7" style="--index-g: 4;"></div>
    <div class="bar bar8" style="--index-h: 5;"></div>
    <div class="bar bar9" style="--index-i: 2;"></div>
  </div>
</body>

</html>

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Here’s a breakdown of the code block above:

Created a root animation to change the value of a variable --t infinitely
Styled the body and container class
Created the initial state for the bar class and declared some variables we would use in our animation. Here we also created a transition property and used round() and mod() CSS functions to generate dynamic values for the background colors of the bars
Next, we applied a height transition to each of the bars, depending on the values obtained from the variables
Finally, we have the HTML element structure

The code above produces the following animation: Optimizing CSS time-based animations with new CSS functions

Recreating the animation with CSS keyframes

In this section, we will rebuild the sound bar animation, but we’ll use animations and CSS keyframes instead:

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Beats Bar Animation with CSS Keyframes</title>
  <style>
    body {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      background-color: #222;
      margin: 0;
    }

    .container {
      height: 500px;
      width: 250px;
      position: relative;
      display: flex;
      gap: 10px;
    }

    .bar {
      position: absolute;
      bottom: 0;
      width: 20px;
      height: 20px;
      --amplitude: 30px;
      --base-height: 20px;
      --frequency: 1;
      transition: height 0.5s ease-in-out;
      animation: bounce 1s infinite;
    }

    @keyframes bounce {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 0.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude));
      }
    }

    .bar1 {
      animation: bounce1 1s infinite, colorChange1 2s infinite;
      margin-left: 10px;
    }

    .bar2 {
      animation: bounce2 1s infinite, colorChange2 2s infinite;
      margin-left: 30px;
    }

    .bar3 {
      animation: bounce3 1s infinite, colorChange3 2s infinite;
      margin-left: 50px;
    }

    .bar4 {
      animation: bounce4 1s infinite, colorChange4 2s infinite;
      margin-left: 70px;
    }

    .bar5 {
      animation: bounce5 1s infinite, colorChange5 2s infinite;
      margin-left: 90px;
    }

    .bar6 {
      animation: bounce6 1s infinite, colorChange6 2s infinite;
      margin-left: 110px;
    }

    .bar7 {
      animation: bounce7 1s infinite, colorChange7 2s infinite;
      margin-left: 130px;
    }

    .bar8 {
      animation: bounce8 1s infinite, colorChange8 2s infinite;
      margin-left: 150px;
    }

    .bar9 {
      animation: bounce9 1s infinite, colorChange9 2s infinite;
      margin-left: 170px;
    }

    @keyframes colorChange1 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(0, 100%, 50%, 1), hsla(180, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(180, 100%, 50%, 1), hsla(360, 100%, 50%, 1));
      }
    }

    @keyframes colorChange2 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(30, 100%, 50%, 1), hsla(210, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(210, 100%, 50%, 1), hsla(390, 100%, 50%, 1));
      }
    }

    @keyframes colorChange3 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(60, 100%, 50%, 1), hsla(240, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(240, 100%, 50%, 1), hsla(420, 100%, 50%, 1));
      }
    }

    @keyframes colorChange4 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(90, 100%, 50%, 1), hsla(270, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(270, 100%, 50%, 1), hsla(450, 100%, 50%, 1));
      }
    }

    @keyframes colorChange5 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(120, 100%, 50%, 1), hsla(300, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(300, 100%, 50%, 1), hsla(480, 100%, 50%, 1));
      }
    }

    @keyframes colorChange6 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(150, 100%, 50%, 1), hsla(330, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(330, 100%, 50%, 1), hsla(510, 100%, 50%, 1));
      }
    }

    @keyframes colorChange7 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(180, 100%, 50%, 1), hsla(360, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(360, 100%, 50%, 1), hsla(540, 100%, 50%, 1));
      }
    }

    @keyframes colorChange8 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(210, 100%, 50%, 1), hsla(390, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(390, 100%, 50%, 1), hsla(570, 100%, 50%, 1));
      }
    }

    @keyframes colorChange9 {

      0%,
      100% {
        background: linear-gradient(to top, hsla(240, 100%, 50%, 1), hsla(420, 100%, 50%, 1));
      }

      50% {
        background: linear-gradient(to top, hsla(420, 100%, 50%, 1), hsla(600, 100%, 50%, 1));
      }
    }

    @keyframes bounce1 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 0.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 1.5);
      }
    }

    @keyframes bounce2 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 1.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 2.5);
      }
    }

    @keyframes bounce3 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 2.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 5);
      }
    }

    @keyframes bounce4 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 4.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 8);
      }
    }

    @keyframes bounce5 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 6.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 10);
      }
    }

    @keyframes bounce6 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 4.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 8);
      }
    }

    @keyframes bounce7 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 2.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 5);
      }
    }

    @keyframes bounce8 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 1.4);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 2.8);
      }
    }

    @keyframes bounce9 {

      0%,
      100% {
        height: calc(var(--base-height) + var(--amplitude) * 0.5);
      }

      50% {
        height: calc(var(--base-height) + var(--amplitude) * 1.6);
      }
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="bar bar1"></div>
    <div class="bar bar2"></div>
    <div class="bar bar3"></div>
    <div class="bar bar4"></div>
    <div class="bar bar5"></div>
    <div class="bar bar6"></div>
    <div class="bar bar7"></div>
    <div class="bar bar8"></div>
    <div class="bar bar9"></div>
  </div>
</body>

</html>

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In the code above, we have styles for the body, container, and bar elements. We added an initial fallback animation state bounce and defined the animation properties with keyframes. Furthermore, we had to create separate keyframes animations for each bar’s height and background color change. The output of this animation is shown below: Optimizing CSS time-based animations with new CSS functions

Creating the animation with JavaScript

Here, we will demonstrate how we can work with HTML, CSS, and JavaScript to recreate the animation in the previous section:

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Beats Bar Animation with JavaScript</title>
  <style>
    body {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      background-color: #222;
      margin: 0;
    }

    .container {
      display: flex;
      gap: 0;
      position: relative;
    }

    .bar {
      width: 20px;
      position: absolute;
      bottom: 0;
      transition: height 0.1s ease-in-out, background 0.1s ease-in-out;
    }

    .bar1 {
      left: 0;
    }

    .bar2 {
      left: 20px;
    }

    .bar3 {
      left: 40px;
    }

    .bar4 {
      left: 60px;
    }

    .bar5 {
      left: 80px;
    }

    .bar6 {
      left: 100px;
    }

    .bar7 {
      left: 120px;
    }

    .bar8 {
      left: 140px;
    }

    .bar9 {
      left: 160px;
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="bar bar1" data-index="1"></div>
    <div class="bar bar2" data-index="2"></div>
    <div class="bar bar3" data-index="3"></div>
    <div class="bar bar4" data-index="4"></div>
    <div class="bar bar5" data-index="5"></div>
    <div class="bar bar6" data-index="6"></div>
    <div class="bar bar7" data-index="7"></div>
    <div class="bar bar8" data-index="8"></div>
    <div class="bar bar9" data-index="9"></div>
  </div>

  <script>
    const bars = document.querySelectorAll('.bar');
    const baseHeight = 100; // Base height of bars
    const amplitude = 150; // Amplitude of height changes
    const frequency = 2; // Frequency of the animation
    const animationSpeed = 0.1; // Speed of the animation

    function animateBars() {
      const currentTime = Date.now() / 1000; // Get the current time in seconds we will use this as a flux value

      bars.forEach((bar, index) => {
        // Calculate the height of the bar based on the current time
        const timeOffset = index * frequency;
        const height = baseHeight + amplitude * Math.abs(Math.sin(currentTime * frequency + timeOffset));
        bar.style.height = `${height}px`;

        const hue = (currentTime * 50) % 360; // Dynamic hue based on time
        const alpha = 1; // alpha of 1 to avoid transparency at any point
        // Set the background color of the bar using a linear gradient
        bar.style.background = `linear-gradient(to top, hsla(${hue}, 100%, 50%, ${alpha}), hsla(${(hue + 180) % 360}, 100%, 50%, ${alpha}))`;
      });

      requestAnimationFrame(animateBars);
    }

    function initializeBars() {
      // Set the initial height and color of the bars
      bars.forEach((bar, index) => {
        const initialHeight = baseHeight + amplitude * Math.abs(Math.sin(index * frequency));
        bar.style.height = `${initialHeight}px`;

        const initialHue = (index * 50) % 360; // Initial hue based on index
        const initialAlpha = 1; // Set initial alpha to 1 to avoid transparency
        bar.style.background = `linear-gradient(to top, hsla(${initialHue}, 100%, 50%, ${initialAlpha}), hsla(${(initialHue + 180) % 360}, 100%, 50%, ${initialAlpha}))`;
      });
    }

    // Initialize the bars with their initial heights and colors
    initializeBars();

    // Start the animation
    animateBars();
  </script>
</body>

</html>

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In the code above, we styled the elements with CSS and created the HTML structure. We used JavaScript to select all elements with the class bar and also declared the variables. Next, we used a set of mathematical calculations to offset the bar height property and apply visual changes to the background gradient. The result is shown in the GIF below: Optimizing CSS time-based animations with new CSS functions

Code comparison

Let’s compare these different methods using certain technical aspects:

Technical aspect	CSS functions	Keyframes	JavaScript
Code length	Generally shorter, making use of variables and functions	Can be lengthy depending on the number of keyframes and the interpolation points defined	The length depends on factors such as the elements to be manipulated, the logic, and properties to be applied.
Ease of implementation	Simple for dynamic, repetitive patterns	Simple for predefined animations	Complex logic handling and interaction
Performance	High performance, offloaded to the GPU, and less CPU-intensive	High performance, offloaded to the GPU, less CPU intensive	Can be less performant, dependent on the JavaScript engine and the amount of JavaScript to be executed on the web
Control	Dynamic and flexible	Static, predefined frames	Highly dynamic and interactive
Maintenance	Easy to maintain, concise syntax	Easy to maintain but can get verbose	Can become complex and harder to maintain, and make changes to the logic
Animation types	Best for simple, repetitive, mathematical animations	Great for detailed, multi-step animations	Best for interactive and responsive animations
Reusability	High reusability with CSS variables since mathematical functions can create different values for the same variable	Moderate, requires duplication for different animations	High reusability with functions and logic
Browser compatibility	`Mod()` and `Round()` are not compatible with Opera and Samsung browsers, the rest are fine	Keyframes have been around for a while, so it will be compatible for time-based animations	JavaScript is compatible with all browsers for time-based animations