Dealing with asynchronous problems in Node.js is a classic issue that many developers face. The findUser() function, for example, has an asynchronous response where the callback is executed at a later time. This can lead to issues when trying to handle the flow of control in your code, especially within loops where multiple requests are made simultaneously.
To tackle this problem, there are different approaches you can take. One common solution involves using promises, which provide a powerful way to manage the flow of asynchronous operations. In cases where promises are not used, a manual approach can be implemented to keep track of pending operations and ensure that all tasks are completed before moving on to the next step.
Manual Approach Solution
// Implementing a manual solution to handle asynchronous operations
var matchAgainstAD = function (stUsers) {
var remaining = stUsers.length;
stUsers.forEach(function (element, i) {
// Function to check if all operations have completed
function checkDone() {
if (remaining === 0) {
postUsers(staleUsers);
}
}
// Find user by sAMAccountName
var ad = new ActiveDirectory(config);
ad.findUser(sAMAccountName, function (err, user) {
--remaining;
if (err) {
console.log('ERROR: ' + JSON.stringify(err));
checkDone();
return;
}
if (!user) {
staleUsers.push(stUsers[i])
}
checkDone();
});
});
}
// Function to post users data
var postUsers = function(staleUsers) {
request.post({
headers: {'content-type' : 'application/x-www-form-urlencoded'},
url: 'http://localhost:8000/api/record/newRecord',
qs: staleUsers
}, function(err, res, body) {
// console.log(body);
})
}
In this manually coded solution, a counter is initialized to track the number of ongoing operations. As each operation completes, the counter is decremented until all tasks are finished. Only then is the postUsers() function called with the accumulated data.
Solution Using Bluebird Promises
Another approach involves utilizing the Bluebird promise library to streamline the handling of asynchronous operations. By promisifying async functions, you can leverage the comprehensive error handling and control flow capabilities provided by promises.
You can adopt a similar strategy using standard ES6 promises built-in to Node.js, albeit with the need to manually create promisified versions of async functions since the built-in functionality found in Bluebird is not available.