Microsoft.Azure.WebJobs.Script.ScriptHost.DeterminePrimaryScriptFile C# (CSharp) Method

        internal static string DeterminePrimaryScriptFile(JObject functionConfig, string[] functionFiles)
        {
            if (functionFiles.Length == 1)
            {
                // if there is only a single file, that file is primary
                return functionFiles[0];
            }
            else
            {
                // First see if there is an explicit primary file indicated
                // in config. If so use that.
                string functionPrimary = null;
                string scriptFileName = (string)functionConfig["scriptFile"];
                if (!string.IsNullOrEmpty(scriptFileName))
                {
                    functionPrimary = functionFiles.FirstOrDefault(p =>
                        string.Compare(Path.GetFileName(p), scriptFileName, StringComparison.OrdinalIgnoreCase) == 0);
                }
                else
                {
                    // if there is a "run" file, that file is primary,
                    // for Node, any index.js file is primary
                    functionPrimary = functionFiles.FirstOrDefault(p =>
                        Path.GetFileNameWithoutExtension(p).ToLowerInvariant() == "run" ||
                        Path.GetFileName(p).ToLowerInvariant() == "index.js");
                }

                return functionPrimary;
            }
        }