[[URL (JavaScript)|URL]]クラスを使う。 ```js > (new URL("favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/bbb/favicon.ico' > (new URL("./favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/bbb/favicon.ico' > (new URL("../favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/favicon.ico' > (new URL("/favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/favicon.ico' > (new URL("favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/bbb/favicon.ico' > (new URL("//favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://favicon.ico/' > (new URL("https://ddd/favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://ddd/favicon.ico' > (new URL("/ddd/favicon.ico", "https://aaa/bbb/ccc")).toString() 'https://aaa/ddd/favicon.ico' ```