modify(api): change the function signature of extract API

src/api.ts

@@ -34,19 +34,12 @@ export function inspect(tree: MfmNode[], action: (node: MfmNode) => void): void
 	}
 }
 
-export function extract(nodes: MfmNode[], type: (MfmNode['type'] | MfmNode['type'][])): MfmNode[] {
+export function extract(nodes: MfmNode[], predicate: (node: MfmNode) => boolean): MfmNode[] {
 	const dest = [] as MfmNode[];
 
 	inspect(nodes, (node) => {
-		if (Array.isArray(type)) {
-			if (type.some(i => i == node.type)) {
-				dest.push(node);
-			}
-		}
-		else {
-			if (type == node.type) {
-				dest.push(node);
-			}
+		if (predicate(node)) {
+			dest.push(node);
 		}
 	});
 

test/api.ts

@@ -42,7 +42,7 @@ after`;
 				MENTION('piyo', null, '@piyo'),
 				MENTION('bebeyo', null, '@bebeyo')
 			];
-			assert.deepStrictEqual(mfm.extract(nodes, 'mention'), expect);
+			assert.deepStrictEqual(mfm.extract(nodes, node => node.type == 'mention'), expect);
 		});
 
 		it('nested', () => {
@@ -52,7 +52,7 @@ after`;
 				EMOJI_CODE('foo'),
 				EMOJI_CODE('piyo')
 			];
-			assert.deepStrictEqual(mfm.extract(nodes, 'emojiCode'), expect);
+			assert.deepStrictEqual(mfm.extract(nodes, node => node.type == 'emojiCode'), expect);
 		});
 	});
 });