How to call function in async

Question

function a() in async function :

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db(mongourl);
    function a (){
      //do something
    }
});

how to trigger a() in another async function?

server.on('clientConnected', function(client) {
    //do a()
});

Answer 1

Make a() a global function:

function a() {
    // body 
}
MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db(mongourl);
    a()
});

server.on('clientConnected', function(client) {
    a()
});