using System;

using System.Text;

using System.Text.RegularExpressions;

public class Program

{

    private static string GetJsFile(string filename) {

        return @"function test1() {

          return 'OK';

        }

        function test2(x) {

          if (x == 2) {

            return 'OK';

          }

        }

        function test3(x,y) {

          var x = '}`\'}';

          var r = /}/;

          // }

          /* } 

            }

          */

        }

        function test4() {

        }";

    }

    private static string GetFunction(string jstext, string functionname) {

​

        var start = Regex.Match(jstext, @"function\s+" + functionname + @"\s*\([^)]*\)\s*{");

        if(!start.Success) {

            throw new Exception("Function not found: " + functionname);     

        }

        StringBuilder sb = new StringBuilder(start.Value);

        jstext = jstext.Substring(start.Index + start.Value.Length);

        var brackets = 1;

        var i = 0;

        var delimiters = "`/'\"";

        string currentDelimiter = null;

        var isEscape = false;

        var isComment = false;

        var isMultilineComment = false;

        while(brackets > 0 && i < jstext.Length) {

            var c = jstext[i].ToString();

            var wasEscape = isEscape;

            if(isComment || !isEscape)

            {

                if(c == @"\") {

                    // Found escape symbol.

                    isEscape = true;

                } else if(i > 0 && !isComment && (c == "*" || c == "/") && jstext[i-1] == '/') {

                    // Found start of a comment block

                    isComment = true;

                    isMultilineComment = c == "*";

                } else if(c == "\n" && isComment && !isMultilineComment) {

                    // Found termination of singline line comment

                    isComment = false;

                } else if(isMultilineComment && c == "/" && jstext[i-1] == '*') {

                    // Found termination of multiline comment

                    isComment = false;

                    isMultilineComment = false;

                } else if(delimiters.Contains(c)) {

                    // Found a string or regex delimiter

                    currentDelimiter = (currentDelimiter == c) ? null : currentDelimiter ?? c;

                }

​

                // The current symbol doesn't appear to be commented out, escaped or in a string

                // If it is a bracket, we should treat it as one

                if(currentDelimiter == null && !isComment) {

                    if(c == "{") {

                        brackets++;

                    }

                    if(c == "}") {

                        brackets--;

                    }

                }

​

            }

            sb.Append(c);

            i++;

            if(wasEscape) isEscape = false;

        }

        return sb.ToString();

    }

    public static void Main()

    {

        var fileContent = GetJsFile("somefile.js");

        for(var i = 1; i < 5; i++) {        

            Console.WriteLine(GetFunction(fileContent, "test" + i));

            Console.WriteLine("-----------------------------------");

        }

    }

}