Jurassic.Compiler.Lexer.ReadIdentifier C# (CSharp) Method

        private Token ReadIdentifier(int firstChar)
        {
            // Process the first character.
            var name = new StringBuilder();
            if (firstChar == '\\')
            {
                // Unicode escape sequence.
                if (ReadNextChar() != 'u')
                    throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid escape sequence in identifier.", this.lineNumber, this.Source.Path);
                firstChar = this.reader.Peek();
                if (firstChar == '{')
                {
                    // ECMAScript 6 extended unicode escape sequence.
                    string extendedCharacter = ReadExtendedUnicodeSequence();
                    if (extendedCharacter.Length == 1 && IsIdentifierChar(extendedCharacter[0]) == false)
                        throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid character in identifier.", this.lineNumber, this.Source.Path);
                    name.Append(extendedCharacter);
                }
                else
                {
                    firstChar = ReadHexEscapeSequence(4);
                    if (IsIdentifierChar(firstChar) == false)
                        throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid character in identifier.", this.lineNumber, this.Source.Path);
                    name.Append((char)firstChar);
                }
            }
            else
                name.Append((char)firstChar);

            // Read characters until we hit the first non-identifier character.
            while (true)
            {
                int c = this.reader.Peek();
                if (IsIdentifierChar(c) == false || c == -1)
                    break;

                if (c == '\\')
                {
                    // Unicode escape sequence.
                    ReadNextChar();
                    if (ReadNextChar() != 'u')
                        throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid escape sequence in identifier.", this.lineNumber, this.Source.Path);
                    c = this.reader.Peek();
                    if (c == '{')
                    {
                        // ECMAScript 6 extended unicode escape sequence.
                        string extendedCharacter = ReadExtendedUnicodeSequence();
                        if (extendedCharacter.Length == 1 && IsIdentifierChar(extendedCharacter[0]) == false)
                            throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid character in identifier.", this.lineNumber, this.Source.Path);
                        name.Append(extendedCharacter);
                    }
                    else
                    {
                        c = ReadHexEscapeSequence(4);
                        if (IsIdentifierChar(c) == false)
                            throw new JavaScriptException(this.engine, ErrorType.SyntaxError, "Invalid character in identifier.", this.lineNumber, this.Source.Path);
                        name.Append((char)c);
                    }
                }
                else
                {
                    // Add the character we peeked at to the identifier name.
                    name.Append((char)c);

                    // Advance the input stream.
                    ReadNextChar();
                }
            }

            // Check if the identifier is actually a keyword, boolean literal, or null literal.
            return KeywordToken.FromString(name.ToString(), this.engine.CompatibilityMode, this.StrictMode);
        }