LibJS: Add spec comments to SymbolPrototype

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/81c6ad047a
Pull-request: https://github.com/SerenityOS/serenity/pull/18336
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibJS/Runtime/SymbolPrototype.cpp

@@ -42,40 +42,58 @@ ThrowCompletionOr<void> SymbolPrototype::initialize(Realm& realm)
 // thisSymbolValue ( value ), https://tc39.es/ecma262/#thissymbolvalue
 static ThrowCompletionOr<Symbol*> this_symbol_value(VM& vm, Value value)
 {
+    // 1. If value is a Symbol, return value.
     if (value.is_symbol())
         return &value.as_symbol();
-    if (value.is_object() && is<SymbolObject>(value.as_object()))
+
+    // 2. If value is an Object and value has a [[SymbolData]] internal slot, then
+    if (value.is_object() && is<SymbolObject>(value.as_object())) {
+        // a. Let s be value.[[SymbolData]].
+        // b. Assert: s is a Symbol.
+        // c. Return s.
         return &static_cast<SymbolObject&>(value.as_object()).primitive_symbol();
+    }
+
+    // 3. Throw a TypeError exception.
     return vm.throw_completion<TypeError>(ErrorType::NotAnObjectOfType, "Symbol");
 }
 
 // 20.4.3.2 get Symbol.prototype.description, https://tc39.es/ecma262/#sec-symbol.prototype.description
 JS_DEFINE_NATIVE_FUNCTION(SymbolPrototype::description_getter)
 {
+    // 1. Let s be the this value.
+    // 2. Let sym be ? thisSymbolValue(s).
     auto* symbol = TRY(this_symbol_value(vm, vm.this_value()));
+
+    // 3. Return sym.[[Description]].
     auto& description = symbol->description();
-    if (!description.has_value())
-        return js_undefined();
-    return PrimitiveString::create(vm, *description);
+    return description.has_value()
+        ? PrimitiveString::create(vm, *description)
+        : js_undefined();
 }
 
 // 20.4.3.3 Symbol.prototype.toString ( ), https://tc39.es/ecma262/#sec-symbol.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(SymbolPrototype::to_string)
 {
+    // 1. Let sym be ? thisSymbolValue(this value).
     auto* symbol = TRY(this_symbol_value(vm, vm.this_value()));
+
+    // 2. Return SymbolDescriptiveString(sym).
     return PrimitiveString::create(vm, TRY_OR_THROW_OOM(vm, symbol->descriptive_string()));
 }
 
 // 20.4.3.4 Symbol.prototype.valueOf ( ), https://tc39.es/ecma262/#sec-symbol.prototype.valueof
 JS_DEFINE_NATIVE_FUNCTION(SymbolPrototype::value_of)
 {
+    // 1. Return ? thisSymbolValue(this value).
     return TRY(this_symbol_value(vm, vm.this_value()));
 }
 
 // 20.4.3.5 Symbol.prototype [ @@toPrimitive ] ( hint ), https://tc39.es/ecma262/#sec-symbol.prototype-@@toprimitive
 JS_DEFINE_NATIVE_FUNCTION(SymbolPrototype::symbol_to_primitive)
 {
-    // The hint argument is ignored.
+    // 1. Return ? thisSymbolValue(this value).
+    // NOTE: The argument is ignored.
     return TRY(this_symbol_value(vm, vm.this_value()));
 }