How to use callback function inside a function?

Question

I want to call a callback function inside a function.so i don't know how to do that

 function call(){
  pg.connect(conString, function(err, client, done) {
    if(err) {
      return console.error('error fetching client from pool', err);
    }
    client.query('INSERT into post1 (data) VALUES ($n)', function(err, result) {
      //call `done()` to release the client back to the pool
      done();

      if(err) {
        return console.error('error running query', err);
      }
      console.log(result.rows[0].number);
      //output: 1
    });
  });
}
board.on("ready", function() {

  // Create a new generic sensor instance for
  // a sensor connected to an analog (ADC) pin
  var sensor = new five.Sensor("A0");

  // When the sensor value changes, log the value
  sensor.on("change", function() {
    var n = this.value();
    //i want to call that function here 
  });
});

and i also want to call this function in another callback function is this the correct way to do or suggest me the right one.

Answer 1

You could do something like this, where you are passing a function into your function. So callback would be a function in this case.

function call(callback){
  pg.connect(conString, function(err, client, done) {
    if(err) {
      return console.error('error fetching client from pool', err);
    }
    client.query('SELECT $1::int AS number', ['1'], function(err, result) {
      //call `done()` to release the client back to the pool
      done();
      callback(); //execute here or wherever
      if(err) {
        return console.error('error running query', err);
      }
      console.log(result.rows[0].number);
      //output: 1
    });
  });
}

then you could call it like

call(function(){
    //some logic here.
})

or:

var someFunction = function()
{
   //do something
}

call(someFunction);