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我正在尝试通过将其格式化为 avif 来优化图像。但是有些浏览器不支持avif。

所以我创建了一个这样的实用函数

  function isAvifSupported() {
    let returnValue;
    const avif = new Image();
    avif.src =
      "data:image/avif;base64,AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0YQAAAAAAAAAoaGRscgAAAAAAAAAAcGljdAAAAAAAAAAAAAAAAGxpYmF2aWYAAAAADnBpdG0AAAAAAAEAAAAeaWxvYwAAAABEAAABAAEAAAABAAABGgAAAB0AAAAoaWluZgAAAAAAAQAAABppbmZlAgAAAAABAABhdjAxQ29sb3IAAAAAamlwcnAAAABLaXBjbwAAABRpc3BlAAAAAAAAAAIAAAACAAAAEHBpeGkAAAAAAwgICAAAAAxhdjFDgQ0MAAAAABNjb2xybmNseAACAAIAAYAAAAAXaXBtYQAAAAAAAAABAAEEAQKDBAAAACVtZGF0EgAKCBgANogQEAwgMg8f8D///8WfhwB8+ErK42A=";
    avif.onload = function () {
        returnValue = true
    };
    return returnValue;
  }

但是当我尝试调用这个函数时，它总是返回未定义的。但是当我使用avif站点中提供的功能时。它工作正常。下面是它的代码

function AddClass(class) { document.documentElement.classList.add(class) };
var avif = new Image();
avif.src = "data:image/avif;base64,AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0YQAAAAAAAAAoaGRscgAAAAAAAAAAcGljdAAAAAAAAAAAAAAAAGxpYmF2aWYAAAAADnBpdG0AAAAAAAEAAAAeaWxvYwAAAABEAAABAAEAAAABAAABGgAAAB0AAAAoaWluZgAAAAAAAQAAABppbmZlAgAAAAABAABhdjAxQ29sb3IAAAAAamlwcnAAAABLaXBjbwAAABRpc3BlAAAAAAAAAAIAAAACAAAAEHBpeGkAAAAAAwgICAAAAAxhdjFDgQ0MAAAAABNjb2xybmNseAACAAIAAYAAAAAXaXBtYQAAAAAAAAABAAEEAQKDBAAAACVtZGF0EgAKCBgANogQEAwgMg8f8D///8WfhwB8+ErK42A=";
avif.onload = function () { AddClass("avif") };
avif.onerror = function () {
  var webp = new Image();
  webp.src = "data:image/webp;base64,UklGRhoAAABXRUJQVlA4TA0AAAAvAAAAEAcQERGIiP4HAA==";
  webp.onload = function () { AddClass("webp") }
}

但是上面定义的函数在dom的顶层添加了css。它必须返回 true 或 false，而不是添加类。这样我就可以像这样轻松处理。


let updatedImageUrl = isAvifSupported() ? `${imageUrl}?fm=avif` ? imageUrl

但我不知道，如何解决这个问题。请推荐一个解决方案。

4

2 回答 2

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您的代码段的主要问题是您没有考虑异步调用。

onload将在函数返回后调用。要解决此问题，您必须提供回调并实现承诺，如下面的示例所示。

function isAvifSupported() {
  return new Promise(resolve => {
      var image = new Image();
  
      image.onload = image.onerror = function() {
        resolve(image.width === 2);
      };
  
      image.src = "data:image/avif;base64,AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0YQAAAAAAAAAoaGRscgAAAAAAAAAAcGljdAAAAAAAAAAAAAAAAGxpYmF2aWYAAAAADnBpdG0AAAAAAAEAAAAeaWxvYwAAAABEAAABAAEAAAABAAABGgAAAB0AAAAoaWluZgAAAAAAAQAAABppbmZlAgAAAAABAABhdjAxQ29sb3IAAAAAamlwcnAAAABLaXBjbwAAABRpc3BlAAAAAAAAAAIAAAACAAAAEHBpeGkAAAAAAwgICAAAAAxhdjFDgQ0MAAAAABNjb2xybmNseAACAAIAAYAAAAAXaXBtYQAAAAAAAAABAAEEAQKDBAAAACVtZGF0EgAKCBgANogQEAwgMg8f8D///8WfhwB8+ErK42A=";
    });
}

isAvifSupported().then(console.log);

作为灵感，我调整了标准的modernizr片段以适合您的用例并使用了您的虚拟图像。

请记住，因为您必须使用异步调用，所以功能检测也必须是异步的。

isAvifSupported().then(
  isSupported => {
    const updatedImageUrl = isSupported ?
      `${imageUrl}?fm=avif` :
      imageUrl;
  }
);

根据您的项目，您可能需要重构一些东西来实现承诺（或回调）解决方案，但不幸的是，无法同步检查 avif 支持。

于 2021-11-11T11:33:15.883 回答
0

以下功能将正常工作。这是@Stefan Judis 的扩展答案版本。我根据我的项目修改了这个

import React, { useEffect, useState } from "react";
import "./styles.css";

const url =
  "https://images.ctfassets.net/{space_id}/1WJFyl9C8q18KI6OQG7mPu/{unique_name}/name.jpg";

const ImageFormat = () => {
  const [imageFormat, setImageFormat] = useState("");

  function addImageProcess(src) {
    return new Promise((resolve, reject) => {
      let img = new Image();
      img.onload = () => resolve("avif");
      img.onerror = () => {
        const webp = new Image();
        webp.src =
          "data:image/webp;base64,UklGRhoAAABXRUJQVlA4TA0AAAAvAAAAEAcQERGIiP4HAA==";
        webp.onload = async () => {
          resolve("webp");
        };

        webp.onerror = () => {
          reject("");
        };
      };
      img.src = src;
    });
  }

  useEffect(() => {
    async function logImageFormat(imageUrl) {
      let imageFormatValue = await addImageProcess(imageUrl);
      setImageFormat(`${url}?fm=${imageFormatValue}&w=3500`);
    }

    logImageFormat(
      "data:image/avif;base64,AAAAIGZ0eXBhdmlmAAAAAGF2aWZtaWYxbWlhZk1BMUIAAADybWV0YQAAAAAAAAAoaGRscgAAAAAAAAAAcGljdAAAAAAAAAAAAAAAAGxpYmF2aWYAAAAADnBpdG0AAAAAAAEAAAAeaWxvYwAAAABEAAABAAEAAAABAAABGgAAAB0AAAAoaWluZgAAAAAAAQAAABppbmZlAgAAAAABAABhdjAxQ29sb3IAAAAAamlwcnAAAABLaXBjbwAAABRpc3BlAAAAAAAAAAIAAAACAAAAEHBpeGkAAAAAAwgICAAAAAxhdjFDgQ0MAAAAABNjb2xybmNseAACAAIAAYAAAAAXaXBtYQAAAAAAAAABAAEEAQKDBAAAACVtZGF0EgAKCBgANogQEAwgMg8f8D///8WfhwB8+ErK42A="
    );
  }, []);

  return (
    <>
      <div className="App">{imageFormat}</div>
    </>
  );
};

export default ImageFormat;
于 2021-11-12T04:25:39.750 回答