Create a field in the result object"distance"

distanceField.js

const getDistance=({lat, lon, query,sortOptions={distance:-1} })=>{
    
  // implementation of the distance calculation using mongodb aggregate pipeline
  //assuming there's a field called businessInfo and it's an object like {location:{lon:value, lat:value}}
    let radlat1 = { $divide: [{ $multiply: [3.141592653589793238, lat] }, 180] };
    let radlat2 = { $divide: [{ $multiply: [3.141592653589793238, "$businessInfo.location.lat"] }, 180] };
    let theta = { $subtract: [lon, "$businessInfo.location.lon"] }; 
    let radtheta = { $divide: [{ $multiply: [3.141592653589793238, theta] }, 180] };
    let dist = { $sum: [{ $multiply: [{ $sin: radlat1 }, { $sin: radlat2 }] }, { $multiply: [{ $cos: radlat1 }, { $cos: radlat2 }, { $cos: radtheta }] }] };
    dist = { $acos: dist };
    dist = { $divide: [{ $multiply: [dist, 180] }, 3.141592653589793238] };
    dist = { $multiply: [dist, 60, 1.1515] };

  
    //if no sortOptions is received, the default value is sort by calculated distance, closest first
    let sort = [
        { $sort: sortOptions },
        {
            $addFields: {
                distance: dist
            }
        }
    ]

    await collection.aggregate([
        { $match: query },
        ...sort
    ]).toArray((err, res)=>{
    // process the result
    })
  
}