The jscript.c use a single RegExp:

static void installJavaScriptRegex (const langType language)
{
    addTagRegex (language, "^[ \t]*function[ \t]*([A-Za-z0-9_]+)[ \t]*\\(",
        "\\1", "f,function,functions", NULL);
}

/* Create parser definition stucture */
extern parserDefinition* JavaScriptParser (void)
{
    static const char *const extensions [] = { "js", NULL };
    parserDefinition *const def = parserNew ("JavaScript");
    def->extensions = extensions;
    def->initialize = installJavaScriptRegex;
    def->regex      = TRUE;
    return def;
}

I will spend sometime to modify the source and re-compile the ctags.exe