indexof() partial match issue

 function FilterResults(keyword){
  
  //connect with spreadsheet
  var ss = SpreadsheetApp.openByUrl(url);
  var ws = ss.getSheetByName("sheet1");
  var sheetData = ws.getRange(1,1,ws.getRange("A1").getDataRegion().getLastRow(),5).getValues();
  
  //create arrays of values from cells in each column   
   var Column1List = sheetData.map(function(r){return r[0]; });
   var Column2List = sheetData.map(function(r){return r[1]; });
   
   
   //make sure search tags are in string format
   var x = keyword.toString();
   
   //find 1st row(position) that has tag in it
   var position = Column2List.indexOf(x);
   
     if (position > -1){
   
   //if the search found a match return cell content according to row number
     return Column1List[position];
   }else{
     return "unavailable";
   }