LibJS: Avoid options object allocation in fromBase64() and toBase64()

When no options (or undefined) are passed into these APIs, the spec has
us synthesize a temporary "options object" to read the options from.

We don't actually need these objects, so let's sidestep the allocation
if we can (and just use the default values in that case).

Author: awesomekling

Libraries/LibJS/Runtime/Uint8Array.cpp

@@ -89,18 +89,23 @@ JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayConstructorHelpers::from_base64)
     if (!string_value.is_string())
         return vm.throw_completion<TypeError>(ErrorType::NotAString, string_value);
 
-    // 2. Let opts be ? GetOptionsObject(options).
-    auto options = TRY(get_options_object(vm, options_value));
-
-    // 3. Let alphabet be ? Get(opts, "alphabet").
-    // 4. If alphabet is undefined, set alphabet to "base64".
-    // 5. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
-    auto alphabet = TRY(parse_alphabet(vm, *options));
-
-    // 6. Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
-    // 7. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
-    // 8. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
-    auto last_chunk_handling = TRY(parse_last_chunk_handling(vm, *options));
+    // OPTIMIZATION: Avoid allocating an empty options object if none was provided.
+    Alphabet alphabet = Alphabet::Base64;
+    AK::LastChunkHandling last_chunk_handling = AK::LastChunkHandling::Loose;
+    if (!options_value.is_undefined()) {
+        // 2. Let opts be ? GetOptionsObject(options).
+        auto options = TRY(get_options_object(vm, options_value));
+
+        // 3. Let alphabet be ? Get(opts, "alphabet").
+        // 4. If alphabet is undefined, set alphabet to "base64".
+        // 5. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+        alphabet = TRY(parse_alphabet(vm, *options));
+
+        // 6. Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
+        // 7. If lastChunkHandling is undefined, set lastChunkHandling to "loose".
+        // 8. If lastChunkHandling is not one of "loose", "strict", or "stop-before-partial", throw a TypeError exception.
+        last_chunk_handling = TRY(parse_last_chunk_handling(vm, *options));
+    }
 
     // 9. Let result be FromBase64(string, alphabet, lastChunkHandling).
     auto result = JS::from_base64(vm, string_value.as_string().utf8_string_view(), alphabet, last_chunk_handling);
@@ -310,17 +315,22 @@ JS_DEFINE_NATIVE_FUNCTION(Uint8ArrayPrototypeHelpers::to_base64)
     // 2. Perform ? ValidateUint8Array(O).
     auto typed_array = TRY(validate_uint8_array(vm));
 
-    // 3. Let opts be ? GetOptionsObject(options).
-    auto options = TRY(get_options_object(vm, options_value));
-
-    // 4. Let alphabet be ? Get(opts, "alphabet").
-    // 5. If alphabet is undefined, set alphabet to "base64".
-    // 6. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
-    auto alphabet = TRY(parse_alphabet(vm, *options));
-
-    // 7. Let omitPadding be ToBoolean(? Get(opts, "omitPadding")).
-    auto omit_padding_value = TRY(options->get(vm.names.omitPadding)).to_boolean();
-    auto omit_padding = omit_padding_value ? AK::OmitPadding::Yes : AK::OmitPadding::No;
+    // OPTIMIZATION: Avoid allocating an empty options object if none was provided.
+    Alphabet alphabet = Alphabet::Base64;
+    AK::OmitPadding omit_padding = AK::OmitPadding::No;
+    if (!options_value.is_undefined()) {
+        // 3. Let opts be ? GetOptionsObject(options).
+        auto options = TRY(get_options_object(vm, options_value));
+
+        // 4. Let alphabet be ? Get(opts, "alphabet").
+        // 5. If alphabet is undefined, set alphabet to "base64".
+        // 6. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+        alphabet = TRY(parse_alphabet(vm, *options));
+
+        // 7. Let omitPadding be ToBoolean(? Get(opts, "omitPadding")).
+        auto omit_padding_value = TRY(options->get(vm.names.omitPadding)).to_boolean();
+        omit_padding = omit_padding_value ? AK::OmitPadding::Yes : AK::OmitPadding::No;
+    }
 
     // 8. Let toEncode be ? GetUint8ArrayBytes(O).
     auto to_encode = TRY(get_uint8_array_bytes(vm, typed_array));