angular-docs-cn/aio/tools/transforms/angular-base-package/post-processors/add-image-dimensions.js

const visit = require('unist-util-visit');
const is = require('hast-util-is-element');
const source = require('unist-util-source');

/**
 * Add the width and height of the image to the `img` tag if they are
 * not already provided. This helps prevent jank when the page is
 * rendered before the image has downloaded.
 *
 * If there is no `src` attribute on an image, or it is not possible
 * to load the image file indicated by the `src` then a warning is emitted.
 */
module.exports = function addImageDimensions(getImageDimensions) {
  return function addImageDimensionsImpl()  {
    return (ast, file) => {
      visit(ast, node => {

        if (is(node, 'img')) {
          const props = node.properties;
          const src = props.src;
          if (!src) {
            file.message('Missing src in image tag `' + source(node, file) + '`');
          } else {
            try {
              const dimensions = getImageDimensions(addImageDimensionsImpl.basePath, src);
              if (props.width === undefined && props.height === undefined) {
                props.width = '' + dimensions.width;
                props.height = '' + dimensions.height;
              }
            } catch(e) {
              if (e.code === 'ENOENT') {
                file.fail('Unable to load src in image tag `' + source(node, file) + '`');
              } else {
                file.fail(e.message);
              }
            }
          }
        }
      });
    };
  };
};