Processing an algorithm as a sequence of nested callbacks is not clever.
TL;DR: Don't process calls in a callback way. Write a sequence.
Problems
Readability
Hard to debug.
Complexity
Solutions
Change callbacks to sequence calls.
Extract repeated Code
Refactor.
Sample Code
Wrong
var fs = require('fs');
var fileWithData = '/hello.world';
fs.readFile(fileWithData, 'utf8', function(err, txt) {
if (err) return console.log(err);
txt = txt + '\n' + 'Add Data!';
fs.writeFile(fileWithData, txt, function(err) {
if(err) return console.log(err);
console.log('Information added');
});
});
Right
var fs = require('fs');
function logTextWasAdded(err) {
if(err) return console.log(err);
console.log('Information added');
};
function addData(error, actualText) {
if (error) return console.log(error);
actualText = actualText + '\n' + 'Add data';
fs.writeFile(fileWithData, actualText, logTextWasAdded);
}
var fileWithData = 'hello.world';
fs.readFile(fileWithData, 'utf8', addData);
Detection
This problem shines at the naked eye. Many linters can detect this complexity and warn us.
Tags
Readability
Complexity
Conclusion
Callback Hell is a very common problem in programming languages with futures or promises.
Callbacks are added in an incremental way. There's no much mess at the beginning.
Complexity without refactoring makes them hard to read and debug.
Relations
There are two ways to write code: write code so simple there are obviously no bugs in it, or write code so complex that there are no obvious bugs in it.
Tony Hoare
This article is part of the CodeSmell Series.