playground: minor improvements

frontend/tools/b64.ts

@@ -0,0 +1,21 @@
+export function b64UrlEncode(data: Uint8Array): string {
+    const base64 = btoa(String.fromCharCode(...data));
+    return base64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+}
+
+export function b64UrlDecode(encoded: string): Uint8Array {
+    // Replace URL-safe characters with standard base64 characters
+    let base64 = encoded.replace(/-/g, '+').replace(/_/g, '/');
+    // Add padding if necessary
+    const padding = base64.length % 4;
+    if (padding) {
+        base64 += '='.repeat(4 - padding);
+    }
+    // Decode the base64 string to a byte array
+    const binaryString = atob(base64);
+    const byteArray = new Uint8Array(binaryString.length);
+    for (let i = 0; i < binaryString.length; i++) {
+        byteArray[i] = binaryString.charCodeAt(i);
+    }
+    return byteArray;
+}