hi i am trying to implement a local orderbook using the binance api however i keep getting this error every now and then it does not always happen but if it does it will happen early on please help

this is the main file that runs calling an exports function from an external file to process the data coming from the web socket on message

wsClient.subscribeSpotDiffBookDepth("btcusdt");
wsClient.on('message', (data) => {

  // Setup and process order book information
  order_book.update_orderbook(data);
  if(order_book.ready === 1){
    order_book.get_orderbook_history();
  }

});

wsClient.on('error', err => {
  /* handle error */
    console.log("this is it 2 " + err);
});

wsClient.on('close', () => {
  /* ... */
});

exports function in external file

exports.update_orderbook = function(data) {
  if(data.e == "depthUpdate"){
    if(this.ready === 0){
      this.ready = 1;
      console.log("Stage 1 in play");
    }else{
      this.buffer += data;
    }

    if(this.ready === 2 && this.asks != null && this.bids != null){
      if(undefined !== this.asks && undefined !== this.bids && undefined !== data.a && undefined !== data.b){
        if(data.U <= this.lastUpdateId + 1 && data.u >= this.lastUpdateId + 1){

      // error is coming from calling this function-------------------------------------------------------
          var temp_array1 = sort_array(this.asks, data.a);
          var temp_array2 = sort_array(this.bids, data.b);
          this.asks = temp_array1;
          this.bids = temp_array2;
          this.lastUpdateId = data.u;

          console.log("Stage 3");
        }
      }
    }else{
      this.buffer += data;
    }
  }
}

function to sort and update the array

function sort_array(array1, array2){
  for(let x in array2){
    if(array2[x][1] == 0){
      for(let i in array2){
        if(array1[i][0] === array2[x][0]){
          array1.splice(i, 1);
        }
      }
    }else{
      var in_array = false;
      for(let i in array1){
        // this seems to be the problem area---------------------------------------------------------
        if(array1[i][0] === array2[x][0]){ 
          array1[i] = array2[x];
          in_array = true;
        }
      }
      if(!in_array){
        array1.push(array2[x]);
      }
    }
  }
  return array1;
}

error log