migrate to typescript

src/lib/file.ts

@@ -0,0 +1,29 @@
+import { isString } from './common.ts';
+
+export function getFileExtension(filename: string): string {
+    if (!filename || !isString(filename)) {
+        return '';
+    }
+
+    const parts = filename.split('.');
+    return parts[parts.length - 1];
+}
+
+export function isFileExtensionSupported(filename: string, supportedExtensions: string): boolean {
+    if (!supportedExtensions) {
+        return false;
+    }
+
+    const supportedExtensionsArray = supportedExtensions.split(',');
+    const fileExtension = getFileExtension(filename).toLowerCase();
+
+    for (let i = 0; i < supportedExtensionsArray.length; i++) {
+        const supportedExtension = getFileExtension(supportedExtensionsArray[i]).toLowerCase();
+
+        if (supportedExtension === fileExtension) {
+            return true;
+        }
+    }
+
+    return false;
+}