code: function ViewabilityContributor(viewabilityAmount) {
    function contributeViewability(ttxRequest) {
      const req = Object.assign({}, ttxRequest);
      const imp = req.imp = req.imp.map(impItem => Object.assign({}, impItem));
      const banner = imp[0].banner = Object.assign({}, imp[0].banner);
      const ext = banner.ext = Object.assign({}, banner.ext);
      const ttx = ext.ttx = Object.assign({}, ext.ttx);
  
      ttx.viewability = { amount: isNaN(viewabilityAmount) ? viewabilityAmount : Math.round(viewabilityAmount) };
  
      return req;
    }
  
    return contributeViewability;
  }
docs: Viewability contribution to request..