Skipping line numbers in lstlisting

Change your definition to

\newcommand*\Reactivatenumber[1]{%
  \setcounter{lstnumber}{\numexpr#1-1\relax}
  \lst@AddToHook{OnNewLine}{%
   \let\thelstnumber\origthelstnumber%
   \refstepcounter{lstnumber}
  }%
}

Full code:

\documentclass{article}
\usepackage{listings}

\lstset{numbers=left,numberblanklines=false,escapeinside=||}
\let\origthelstnumber\thelstnumber
\makeatletter
\newcommand*\Suppressnumber{%
  \lst@AddToHook{OnNewLine}{%
    \let\thelstnumber\relax%
     \advance\c@lstnumber-\@ne\relax%
    }%
}

\newcommand*\Reactivatenumber[1]{%
  \setcounter{lstnumber}{\numexpr#1-1\relax}
  \lst@AddToHook{OnNewLine}{%
   \let\thelstnumber\origthelstnumber%
   \refstepcounter{lstnumber}
  }%
}


\makeatother

\begin{document}
First listing:
\begin{lstlisting}[firstnumber=1]
var myFunc = function() {|\Suppressnumber|
    //my function does many great things
    //and it's only 10 lines long!|\Reactivatenumber{12}|
}

var oneMoreFunc = function() {
    return myFunc;
}

}

var oneMoreFunc = function() {
    return myFunc;
}
\end{lstlisting}
One more listing:
\begin{lstlisting}[firstnumber=18]
var something = "bla";
console.log(something);

}

var oneMoreFunc = function() {
    return myFunc;
}
\end{lstlisting}
\end{document}