async-waterfall-example.js

async.waterfall([
  function(callback) {
    callback(null, 'Task 1', 'Task 2');
  },
  function(arg1, arg2, callback) {
    // arg1 now equals 'Task 1' and arg2 now equals 'Task 2'
    let arg3 = arg1 + ' and ' + arg2;
    callback(null, arg3);
  },
  function(arg1, callback) {
    // arg1 now equals 'Task1 and Task2'
    arg1 += ' completed';
    callback(null, arg1);
  }
], function(err, result) {
  // result now equals to 'Task1 and Task2 completed'
  console.log(result);
});

// Or, with named functions:
async.waterfall([
  myFirstFunction,
  mySecondFunction,
  myLastFunction,
], function(err, result) {
  // result now equals 'Task1 and Task2 completed'
  console.log(result);
});

function myFirstFunction(callback) {
  callback(null, 'Task 1', 'Task 2');
}
function mySecondFunction(arg1, arg2, callback) {
  // arg1 now equals 'Task 1' and arg2 now equals 'Task 2'
  let arg3 = arg1 + ' and ' + arg2;
  callback(null, arg3);
}
function myLastFunction(arg1, callback) {
  // arg1 now equals 'Task1 and Task2'
  arg1 += ' completed';
  callback(null, arg1);
}