There Is No Callback Hell In JavaScript
There is no “callback hell” in Javascript, it is just a bad programming style. The infamous JavaScript “callback hell” can easily be fixed by un-nesting all the callbacks into separate functions.
Here is an example:
const verifyUser = function(username, password, callback) {
dataBase.verifyUser(username, password, function(error, userInfo) {
if (error) {
callback(error);
} else {
dataBase.getRoles(username, function(error, roles) {
if (error) {
callback(error);
} else {
dataBase.logAccess(username, function(error) {
if (error) {
callback(error);
} else {
callback(null, userInfo, roles);
}
})
}
})
}
})
};
The same code with separate functions instead of inline callbacks:
const verifyUser = function(username, password, callback) {
dataBase.verifyUser(username, password, function(error, userInfo) {
if (error) return callback(error);
getRoles(username, userInfo, callback);
}
}
const getRoles = function(username, userInfo, callback) {
dataBase.getRoles(username, function(error, roles) {
if (error) return callback(error);
logAccess(username, userInfo, roles, callback);
})
}
const logAccess = function(username, userInfo, roles, callback) {
dataBase.logAccess(username, function(error) {
if (error) return callback(error);
callback(null, userInfo, roles);
})
}
It is much more readable, manageable and reusable than the approach with inline functions. In fact, there is no “callback hell” in here - there are simply no nested callbacks in this code anymore.
This way, the “callback hell” is simply a bad style of writing code that is easy to avoid.
Libraries like step, async, promises or async/await all provide a way to manage the asynchronous code. These methods may be less verbose or more convenient than “regular” callback functions, but callbacks can work too.
