✨ add lyrics fetching

src/YTMusic.ts

@@ -346,6 +346,23 @@ export default class YTMusic {
 		return video
 	}
 
+	/**
+	 * Get lyrics of a specific Song
+	 * 
+	 * @param videoId Video ID
+	 * @returns Lyrics
+	 */
+	public async getLyrics(videoId: string) {
+		if (!videoId.match(/^[a-zA-Z0-9-_]{11}$/)) throw new Error("Invalid videoId")
+		const data = await this.constructRequest("next", { videoId })
+		const browseId = traverse(traverseList(data, "tabs", "tabRenderer")[1], "browseId")
+
+		const lyricsData = await this.constructRequest("browse", { browseId })
+		const lyrics = traverseString(lyricsData, "description", "runs", "text")()
+
+		return lyrics ? lyrics.replaceAll("\r", "").split("\n") : null
+	}
+
 	/**
 	 * Get all possible information of an Artist
 	 *

src/tests/traversing.spec.ts

@@ -21,10 +21,10 @@ const errors: Problem[] = []
 const queries = ["Lilac", "Weekend", "Eill", "Eminem", "Lisa Hannigan"]
 const expect = (data: any, type: Type) => {
 	const result = type(data)
-	if (!result.data && "problems" in result) {
+	if (!result.data && result.problems?.length) {
 		errors.push(...result.problems!)
 	}
-	equal(!!result.data, true)
+	equal(result.problems, undefined)
 }
 
 const ytmusic = new YTMusic()
@@ -67,6 +67,12 @@ queries.forEach(query => {
 			expect(results, arrayOf(SearchResult))
 		})
 
+		it("Get lyrics of the first song result", async () => {
+			const songs = await ytmusic.searchSongs(query)
+			const lyrics = await ytmusic.getLyrics(songs[0]!.videoId)
+			expect(lyrics, type("string[]|null"))
+		})
+
 		it("Get details of the first song result", async () => {
 			const songs = await ytmusic.searchSongs(query)
 			const song = await ytmusic.getSong(songs[0]!.videoId)