Here’s a reusable function that I think is pretty clear. var Q = require(“q”); // `condition` is a function that returns a boolean // `body` is a function that returns a promise // returns a promise for the completion of the loop function promiseWhile(condition, body) { var done = Q.defer(); function loop() { // When … Read more
render() method should render UI from this.props and this.state, so to asynchronously load data, you can use this.state to store imageId: imageUrl mapping. Then in your componentDidMount() method, you can populate imageUrl from imageId. Then the render() method should be pure and simple by rendering the this.state object Note that the this.state.imageUrls is populated asynchronously, … Read more
I guess this was added in a recent version of Angular but there seems to be now an $$state object on the promise: var deferred = $q.defer(); console.log(deferred.promise.$$state.status); // 0 deferred.resolve(); console.log(deferred.promise.$$state.status); //1 As noted in the comments this is not recommended as it might break when upgrading your Angular version.
Use a pattern along these lines: function getValue(file) { return lookupValue(file); } getValue(‘myFile.txt’).then(function(res) { // do whatever with res here }); (although this is a bit redundant, I’m sure your actual code is more complicated)
Calling $q.when takes a promise or any other type, if it is not a promise then it will wrap it in a promise and call resolve. If you pass a value to it then it is never going to be rejected. From the docs: Wraps an object that might be a value or a (3rd … Read more
In javascript there are no block-level scopes only function-level scopes: Read this article about javaScript Scoping and Hoisting. See how I debugged your code: var deferred = $q.defer(); deferred.count = i; console.log(deferred.count); // 0,1,2,3,4,5 –< all deferred objects // some code .success(function(data){ console.log(deferred.count); // 5,5,5,5,5,5 –< only the last deferred object deferred.resolve(data); }) When you … Read more
You can’t resolve a promise with multiple properties just like you can’t return multiple values from a function. A promise conceptually represents a value over time so while you can represent composite values you can’t put multiple values in a promise. A promise inherently resolves with a single value – this is part of how … Read more
this is always the object the method is called on. However, when passing the method to then(), you are not calling it! The method will be stored somewhere and called from there later. If you want to preserve this, you will have to do it like this: .then(() => this.method2()) or if you have to … Read more
The old adage goes that you should pick the right tool for the job. ES6 promises provide the basics. If all you ever want or need is the basics, then that should/could work just fine for you. But, there are more tools in the tool bin than just the basics and there are situations where … Read more
In simple terms, inside a then handler function: A) When x is a value (number, string, etc): return x is equivalent to return Promise.resolve(x) throw x is equivalent to return Promise.reject(x) B) When x is a Promise that is already settled (not pending anymore): return x is equivalent to return Promise.resolve(x), if the Promise was … Read more