JavaScript is a functional language. It means that functions are at the core of what we program. We can see that in the case of callbacks, where we pass functions as parameters.

function doWorkAndCallBack(data, callback) {
  // does a lot of work, using the data variable

  // no really - A LOT. OF. WORK

  // and then finally
  callback('I am done!');
}

Very often these callback functions are written “inline”, meaning in the place we call doWorkAndCallBack, like this for example:

doWorkAndCallBack('a string of data', function (status) {
  console.log(status);
});

Not seldom we will call callback functions inside the callback function and then get a callback-function that we need to call in order to … it can become pretty messy. Fast.

And when the last 7 lines of your code file look like this:

            });
          });
        });
      });
    });
  });
});

… it’s easy to get lost.

The tip

One simple trick that helped me in my early days (and still do) is to write the function calls in steps. Like this:

I say to myself: “Ok - we are going to call doWorkAndCallBack” And then write this

doWorkAndCallBack();

“It takes two parameters, data and a callback function”

doWorkAndCallBack('', function (){});

“And that callback function will give me a status of some kind. Better add that parameter.”

doWorkAndCallBack('', function (status){});

I then, and here is the magic part, position myself between the { and } and hit ENTER. TA-DA!

doWorkAndCallBack('', function (status){

});

And now I can start to fill out the inside of the callback, what is going to happen once we get back here