如何调试 CSS calc() 值？

Question

我有相对复杂的公式，例如transform: scale(var(--image-scale)) translateY(calc((1px * var(--element-height) * (var(--image-scale) - 1)) / 2 * var(--scrolled-out-y)))

如何调试计算值？ 此外，有没有办法验证/突出显示公式错误？

我试图像这样输出到伪元素但没有运气

    position: fixed;
    display: block;
    left:0;
    right: 0;
    background: yellow;
    padding: 5px;
    z-index: 100;
    content: calc((1px * var(--element-height) * (var(--image-scale) - 1)) / 2 * var(--scrolled-out-y));

我发现的唯一方法是将部分计算放到未使用的数字属性中，例如background-position-x 在下面的 gif 上，因此它将在计算选项卡上显示计算值 - 有用但不是很方便（注意 background-position-x 在页面滚动时更改）：

var sc = ScrollOut({
    cssProps: true
  })
  const results = Splitting();

  var parallaxedElements = document.querySelectorAll('.section');

  document.addEventListener('scroll', function(e) {
    parallaxedElements
    Array.from(parallaxedElements).forEach((el) => {
      var bcr = el.getBoundingClientRect();
      if (bcr.y < 0 && Math.abs(bcr.y) <= bcr.height) {
        el.style.setProperty("--scrolled-out-y", Math.round(Math.abs(bcr.y) * 10000 / bcr.height) / 10000);
      }
    });

  })

@import url("https://fonts.googleapis.com/css?family=Roboto");
  html {
    scroll-behavior: smooth;
  }
  
  body {
    font-family: "Roboto";
    font-size: 14px;
    line-height: 1.4;
    scroll-behavior: smooth;
  }
  
  .section {
    position: relative;
    background-attachment: fixed;
    z-index: 1;
    --image-scale: 1.2;
    --scrolled-out-y: 0;
  }
  
  .section__background {
    position: -webkit-sticky;
    position: sticky;
    top: 0;
    width: 100%;
    height: 100vh;
    overflow: hidden;
  }
  
  .section__background:after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    top: 0;
    z-index: 1;
    background: linear-gradient(to bottom, black, 100% white);
    background: rgba(0, 0, 0, 0.4);
    opacity: calc(1 + ((var(--viewport-y) * 1.5)));
  }
  
  .section__background>img {
    height: 150vh;
    width: 100%;
    object-fit: cover;
    position: absolute;
    left: 0;
    top: 0px;
    user-select: none;
    transform: scale(var(--image-scale)) translateY(calc((-1px * var(--element-height) * (var(--image-scale) - 1)) * var(--scrolled-out-y)));
  }
  /* .indicator:after {
        position: fixed;
        display: block;
        left: 0;
        right: 0;
        background: pink;
        padding: 5px;
        z-index: 100;
        content: calc((1px * var(--element-height) * (var(--image-scale) - 1)) / 2 * var(--scrolled-out-y));
    } */
  
  .section__container {
    padding-bottom: 50vh;
    overflow: hidden;
    align-items: flex-start;
    position: relative;
    z-index: 4;
  }
  
  .section__heading {
    color: #fff;
    text-transform: uppercase;
    font-size: 45px;
    line-height: 1.2;
    font-weight: 800;
    letter-spacing: 8px;
    margin: 0;
    overflow: hidden;
    position: relative;
    padding-bottom: 50px;
    margin-bottom: 50px;
  }
  
  .section__heading:after {
    content: "";
    position: absolute;
    top: 200px;
    left: 0;
    right: 0;
    height: 2px;
    transform: translateX(calc(var(--scrolled-out-y) * 100% - 70%));
    background: #b38c6b;
  }
  
  .section__content {
    display: flex;
    color: white;
    flex-direction: column;
  }
  
  .section__content p+p {
    margin-top: 20px;
  }
  
  .splitting {
    --char-percent: calc(var(--char-index) / var(--char-total));
  }
  
  .splitting .char {
    display: inline-block;
    opacity: calc(1 + ((var(--viewport-y) * 1.5) - var(--char-percent)));
  }

<link rel='stylesheet' href='https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.3/css/bootstrap.min.css'>
<link rel='stylesheet' href='https://unpkg.com/splitting/dist/splitting.css'>

<section data-scroll class="section section-1">
  <div class="section__background">
    <div class="indicator"></div>
    <img src="https://picsum.photos/1920/1079" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>

<section data-scroll class="section section-2">
  <div class="section__background">
    <img src="https://picsum.photos/1920/1081" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>

<section data-scroll class="section section-3">
  <div class="section__background">
    <img src="https://picsum.photos/1920/1082" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>


<section data-scroll class="section section-4">
  <div class="section__background">
    <img src="https://picsum.photos/1920/1083" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>

<section data-scroll class="section section-5">
  <div class="section__background">
    <img src="https://picsum.photos/1920/1084" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>


<section data-scroll class="section section-6">
  <div class="section__background">
    <img src="https://picsum.photos/1920/1085" alt="placeholder image" />
  </div>
  <div class="container section__container">
    <div class="row">
      <div class="title-block col-md-6 d-flex">
        <h1 data-scroll data-splitting class="section__heading">
          Why <br>CSS <br>matters
        </h1>
      </div>
      <div class="col-md-6 d-flex">
        <div class="section__content">
          <p>
            MThe ability to use variables in CSS is a useful and powerful feature that web developers have long been asking for. Well, it has finally arrived, and it’s awesome!
          </p>
          <p>
            In this article we’ll look at the history, importance, and use of CSS variables, and how you can leverage them to make your CSS development and maintenance faster and easier.
          </p>
          <p>
            Keep reading and you will understand why.
          </p>
          <div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>
<script src='https://unpkg.com/scroll-out/dist/scroll-out.min.js'></script>
<script src='https://unpkg.com/splitting@1.0.0/dist/splitting.js'></script>

Answer 1

所以要实际调试 CSS 变量，您可以使用我在下面添加的帮助程序类。

然后在控制台中设置和读取变量，如下所示：

CssVariables.setRootVar('--column-max-width', 'calc((90vw - var(--zoomer-width)) / (var(--columns-shown) + 1))');
console.log('width:', CssVariables.getRootVar("--column-max-width"));

请注意，当您读取变量时，var(--) 已经解析。

当公式无效时，您可能会在控制台上收到警告。

CssVariables.setRootVar('--column-max-width', 'calc(123px - var(123))');
// -> invalid value, declaration skipped

当你例如使用不存在的变量，读取时会得到空字符串。

CssVariables.setRootVar('--column-max-width', 'calc(123px - var(--wtf))');
console.log('width:', CssVariables.getRootVar("--column-max-width"));
// -> width: <empty string>

CssVariables 助手

/**
 * CSS variables helper.
 */
class CssVariables {
    /**
     * Get :root variable.
     * @param {String} name Name of CSS var. e.g. "--columns-shown".
     * @returns {String} Current value.
     */
    static getRootVar(name) {
        return this.getVar(document.documentElement, name);
    }
    /**
     * @see #getRootVar
     */
    static getVar(element, name) {
        return window.getComputedStyle(element, null).getPropertyValue(name);
    }
    /**
     * Set :root variable.
     * @param {String} name Name of CSS var. e.g. "--columns-shown".
     * @param {String} value New value. Should be a strin, but numbers would work as well.
     */
    static setRootVar(name, value) {
        this.setVar(document.documentElement, name, value);
    }
    /**
     * @see #setRootVar
     */
    static setVar(element, name, value) {
        element.style.setProperty(name, value);
    }
}

// if you are working with modules
//export { CssVariables }

Answer 2

有没有办法验证/突出显示公式错误？

在定义公式时，您需要检查是否违反了任何规则。来自the specification：

在每个运算符处，检查左右参数的类型是否存在这些限制。如果兼容，则类型解析如下所述（为简单起见，以下忽略运算符的优先规则）：

• 在+ 或-，检查两侧是否具有相同的类型，或者一侧是<number>，另一侧是<integer>。如果双方是同一类型，则解析为该类型。如果一侧是<number>，另一侧是<integer>，请解析为<number>。
• 在*，检查至少一侧是<number>。如果双方都是<integer>，则解析为<integer>。否则，解析为对方的类型。
• 在/，检查右侧是否为<number>。如果左侧是<integer>，则解析为<number>。否则，解析为左侧的类型。

如果运算符没有通过上述检查，则表达式无效

一开始可能听起来有点复杂，但规则很简单，我们可以用简单的话重写如下：

• 不能加/减两种不同的类型（5px + 5s 没有意义）。
• 只能与数字相乘（5px * 5px 没有意义，不等于25px）。
• 只能用不是0 的数除（5px / 5px 没有意义，不等于1 或1px）。

如果您没有违反任何这些规则，那么您的公式就是正确的。我们不要忘记另一个重要的语法规则：

此外，+ 和 - 运算符的两边都需要空格。 （可以使用 * 和 / 操作符，它们周围没有空格。）

---

考虑到这一点，您只需要确定您的 CSS 变量是数字/整数还是使用类型（长度、频率、角度或时间）定义。如果未定义或包含字符串值，则 calc() 将无效。

查看规范以获取更多详细信息和更准确的解释：https://drafts.csswg.org/css-values-3/#calc-type-checking

---

如何调试计算值？

要检查计算的值，我认为没有办法，因为 calc() 的计算值可能会有所不同，具体取决于您使用它的位置（哪个属性）。换句话说，final 值直到在属性中使用后才存在。

我们可能认为有些公式是微不足道的，例如 calc(5px + 5px)，它总是会计算到 10px，但其他公式会更难。就像calc(5px + 50%) 一样，% 的行为会因属性而异。考虑到这一点，浏览器将永远不会计算该值，直到它在属性中使用。

即使使用 JS，你也无法获得想要调试的 final 值；你只能得到属性的计算值：

var elem = document.querySelector(".box");
var prop = window.getComputedStyle(elem,null).getPropertyValue("--variable");
var height = window.getComputedStyle(elem,null).getPropertyValue("height");
console.log(prop);
console.log(height);

.box {
  --variable: calc(5px + 5px);
  height:var(--variable);
}

<div class="box"></div>