First difference: Sometimes you don’t want to catch errors at the place they arise, but in the code that uses this function, so you don’t catch them. In that case you can’t substitute then() and finally(). Sometimes you have to clean something up whether there was an error or not (nulling references, clearing timeouts … … Read more
Rule of Thumb Whenever you have a doubt about how to do something with promises – think about the synchronous version. try{ var result = myFn(param); // business logic with result } catch(e) { //error handling logic } This, at least to me looks a lot cleaner than a callback with a first parameter that … Read more
The following should work: var request = Promise.promisify(require(“request”)); Promise.promisifyAll(request); Note that this means that request is not a free function since promisification works with prototype methods since the this isn’t known in advance. It will only work in newer versions of bluebird. Repeat it when you need to when forking the request object for cookies. … Read more
No, they won’t. They only bubble up to the result promise if you chain your promises, for which you need to return the inner promises created by the callbacks. Otherwise the outer promise cannot wait for them and will not know when/how they resolve (whether they fulfill or reject). temporaryUserModel.findOne({email: req.body.email}).then(tempUser => { if (tempUser) … Read more
Florian provided a good answer For the sake of your original question, there are several ways to start a chain with Bluebird. One of the simplest is calling Promise.resolve() on nothing: var queue = Promise.resolve(); //resolve a promise with nothing or cast a value or Promise.try(function(…){ return …//chain here }); So you can do: var … Read more
Welcome to the wonderful world of promises. How then works in your example Your assertion in 1 is correct. We can simulate a promise resolving in Bluebird using Promise.resolve on a value. Let’s show this: Let’s get a function that returns a promise: function foo(){ return Promise.resolve(“Value”); } foo().then(alert); This short snippet will alert “Value” … Read more
I think you’re looking for (conditionA ? fs.writeFileAsync(file, jsonData) : Promise.resolve()) .then(functionA); which is short for var waitFor; if (conditionA) waitFor = fs.writeFileAsync(file, jsonData); else waitFor = Promise.resolve(undefined); // wait for nothing, // create fulfilled promise waitFor.then(function() { return functionA(); });
The issue with your code The problem with the above approach is that if you forget releasing the connection after every single time you perform getDb you have a resource leak that might freeze your app eventually when it runs out of the resource you’re leaking. You might, in one place do: var users = … Read more
This is possible, and even quite easy! Well, if we look at how Angular’s own promises work, we need to get Bluebird to $evalAsync somewhere in order to get the exact same behavior. If we do that, the fact both implementations are Promises/A+ compliant means we can interop between $q code and Bluebird code, meaning … Read more
NO you can’t get the data synchronously out of a promise like you suggest in your example. The data must be used within a callback function. Alternatively in functional programming style the promise data could be map()ed over. If your are OK using async/await (you should it’s awesome) then you can write code that looks … Read more