ie11 polyfill基於圖片源集加載背景圖像

Question

我為編寫了以下polyfill，以便可以使用CSS object-fit ：

 const $images = $('.object-fit'); const replacementClass = 'object-fit-replacement'; if ($images.length) { $images.each(function(index, item) { const $image = $(item); // this code will not run in IE if image is in the cache $image.on('load', function(e) { makeDiv(e.currentTarget); }); // this code will run if image is already in the cache if (item.complete) { makeDiv(item); } }); } function makeDiv(image) { const $image = $(image); const $picture = $image.closest('picture'); let $div; let $parent; let imageSource; if ($picture.length) { $parent = $picture.parent(); imageSource = $image.prop('currentSrc') || image.src; } else { $parent = $image.parent(); imageSource = image.src; } $div = $parent.find('.' + replacementClass); if (!$div.length) { $div = $('<div class="' + replacementClass + '"></div>'); $parent.append($div); } $div.css('background-image', 'url(' + imageSource + ')'); $picture.hide(); $image.hide(); } 

 .object-fit-replacement { /* for test only */ background-size:cover; width:100vw; height:100vh; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <picture> <source srcset="https://via.placeholder.com/300x100" media="(max-width:768px)"> <source srcset="https://via.placeholder.com/600x300" media="(min-width:768px)"> <img src="https://via.placeholder.com/200x200" alt="Test" class="image object-fit"> </picture> 

但是，它似乎僅從image標簽加載實際的圖像源。 有沒有辦法尊重當前資源（取自圖片標簽中正確的媒體查詢）-我以為$image.prop('currentSrc')是要獲取它的，但似乎在ie11中不起作用（如果您使用的是chrome，則會加載正確的背景圖片）

Answer 1

這是由於ie11無法處理像素。 最后，由於我知道我們網站上所有圖片元素的斷點（並且它們不會更改，因為它們是由服務器端幫助程序創建的），所以我添加了一些jquery以獲取正確的源從圖片標簽中：

import $ from 'jquery';
import elementHelper from '../helpers/element-helper';
import throttle from 'lodash/throttle';

$(() => {
  const $images = $('.object-fit');
  const replacementClass = 'object-fit-replacement';
  const $window = $(window);

  if ($images.length) {
    $images.each((index, item) => {
      const $image = $(item);
      let imageLoaded = false;

      // this code will not run in IE if image is in the cache
      $image.on('load', e => {
        if (!imageLoaded) {
          makeDiv(e.currentTarget);
          imageLoaded = true;
        }
      });

      // this code will run if image is already in the cache
      if (item.complete && !imageLoaded) {
        makeDiv(item);
        imageLoaded = true;
      }
    });
  }

  $window.on('resize', throttle(() => {
    $(`.${replacementClass}`).each((index, item) => {
      const $picture = $(item).prev('picture');
      console.log('resize', $picture.length)
      if ($picture.length) {
        $div.css('background-image', `url(${getPictureSource($picture)})`);
      }
    });
  }, 100));

  function makeDiv(image) {
    const $image = $(image);
    const $picture = $image.closest('picture');
    let $div;
    let $parent;
    let imageSource;

    if ($picture.length) {
      $parent = $picture.parent();
      imageSource = getImageSource($picture, $image);
    } else {
      $parent = $image.parent();
      imageSource = image.src;
    }

    $div = $parent.find(`.${replacementClass}`);
    if (!$div.length) {
      $div = $(elementHelper.createElement('div', replacementClass));
      $parent.append($div);
    }

    $div.css('background-image', `url(${imageSource})`);

    $picture.hide();
    $image.hide();
  }

  function getImageSource($picture, $image) {
    const imageSource = $image.prop('currentSrc');

    if (imageSource) {
      return imageSource;
    } else {
      return  getPictureSource($picture);
    }
  }

  function getPictureSource($picture) {
    // this assumes that the image helper has created the object fit picture tag and is using the standard 5 media queries
    const $sources = $picture.children('source');
    if ($sources.length === 5) {
      const windowWidth = $window.outerWidth();
      if (windowWidth < 380) {
        return $sources.eq(0).attr('srcset');
      } else if (windowWidth >= 380 && windowWidth < 767) {
        return $sources.eq(1).attr('srcset');
      } else if (windowWidth >= 767 && windowWidth < 1200) {
        return $sources.eq(2).attr('srcset');
      } else if (windowWidth >= 1200 && windowWidth < 1600) {
        return $sources.eq(3).attr('srcset');
      } else {
        return $sources.eq(4).attr('srcset');
      }
    }
    return  $sources.last().attr('srcset'); // this assumes sources are done normally with desktop largest last (default to dektop)
  }
});