node js callback inside for loop code example

Example 1: node js callback

function processData (callback) {
  fetchData(function (err, data) {
    if (err) {
      console.log("An error has occurred. Abort everything!");
      return callback(err);
    }
    data += 1;
    callback(null, data);
  });
}

processData(function (err, data) {
  if (err) {
      console.err(err);
  } else {
    console.log("Data: " + data);
  }
});

Example 2: javascript iterator callback

//use let keywork and i will increment correctly inside loops
for (let i = 0; i < a.length; i++) {
   makeHttpReqest("http://www.codegrepper.com", function(response) {
       // i will increment correctly here; 
 
  });
}

//Alternatively, if you can't use let, this syntax will work too
for (var i = 0; i < a.length; i++) (function(i)
{
   makeHttpReqest("http://www.codegrepper.com", function(response) {
       // i will increment correctly here; 
 
  });
}) (i);