index.js

var fs = require('hexo-fs');
var fm = require('hexo-front-matter');

var absolute_path_reference_url = function(url) {
	url = new URL(url);
	return url.pathname + url.search + url.hash;
};

var contentJsonPath = hexo.public_dir + 'content.json';
var post_asset_folder = hexo.config.post_asset_folder;
var imagesPath = hexo.config.url + hexo.config.root;
var config = hexo.config.hasOwnProperty('featured_image')
	? hexo.config.featured_image
	: {};
// https://tools.ietf.org/html/rfc3986#section-4.2
var useAbsolutePathReference = config.absolute_path_reference;
if (useAbsolutePathReference) {
	imagesPath = absolute_path_reference_url(imagesPath);
}
if (!post_asset_folder) {
	if (hexo.config.image_dir) {
		imagesPath += hexo.config.image_dir;
	} else {
		imagesPath += 'images';
	}
	imagesPath += '/';
}

hexo.extend.filter.register('before_post_render', function(data) {
	var front = fm.parse(data.raw);
	var featured_image = front.featured_image;
	if (featured_image) {
		var thumbnail = front.thumbnail;
		var imagePrefix = imagesPath;
		// Use post asset folder
		if (post_asset_folder) {
			imagePrefix = data.permalink;
			if (useAbsolutePathReference) {
				imagePrefix = absolute_path_reference_url(imagePrefix);
			}
		}
		// Check if the featured image path is an absolute URI
		if (
			featured_image.indexOf('http') === 0 ||
			featured_image.indexOf('/') === 0
		) {
			// Use no prefix since we have the full or relative URI
			imagePrefix = '';
		}

		// Compile the featured image URI
		data.featured_image = imagePrefix + featured_image;

		if (thumbnail) {
			data.thumbnail = imagePrefix + thumbnail;
		}
	}
	return data;
});

hexo.extend.filter.register('before_exit', function() {
	// to work smoothly with hexo_generator_json_content
	var jsonContentCfg = hexo.config.hasOwnProperty('jsonContent')
		? hexo.config.jsonContent
		: {
				meta: true,
		  };
	var postsCfg = jsonContentCfg.hasOwnProperty('posts')
		? jsonContentCfg.posts
		: {};

	if (postsCfg.featured_image && fs.existsSync(contentJsonPath)) {
		var postsObject = {};
		var posts = hexo.locals.get('posts');
		posts.forEach(function(post) {
			postsObject[post.path] = post;
		});
		var content = JSON.parse(fs.readFileSync(contentJsonPath));
		var contentPosts = content.posts;
		if (!contentPosts) return;
		content.posts = contentPosts.map(function(post) {
			var fullPost = postsObject[post.path];
			if (fullPost && fullPost.featured_image) {
				post.featured_image = fullPost.featured_image;
				if (postsCfg.thumbnail && fullPost.thumbnail) {
					post.thumbnail = fullPost.thumbnail;
				}
			}
			return post;
		});
		fs.writeFileSync(contentJsonPath, JSON.stringify(content));
	}
});