Get Prototype's Variable

Question

I want read one variable from prototype.

Normally this variable generating in endgame. But i want read in-game.

JS is here: https://paste.ee/p/4mv8e It's for Chess.com

I see this part in over ChessCom function:

downloadPgn: function(e) {
    this._findFenPgn();
     
    var t = this._getPgnFileName();
     
    return SaveText(this._fenPgn, t, "application/x-chess-pgn;charset=utf-8"), !1
},

I need reach _fenPgn value from console.

I was try console.log(ChessCom.prototype._fenPgn); but fails.

Thanks.