So here’s an oxymoron: I want to create an asynchronous blocking queue in javascript/typescript (if you can implement it without typescript, that’s fine). Basically I want to implement something like Java’s BlockingQueue expect instead of it actually being blocking, it would be async and I c…
Tag: promise
Struggle with chaining of promises in react application
JavaScript, React – sending multiple simultaneous ajax calls struggling with promises. Basically I want to chain the calls, if one server call completes then only do next call, and collect the successful response of calls from endpoint /pqr made inside makeServerCalls. Error: expected to return a value …
Using await within a Promise
There seems something inherently wrong with having to define a Promise’s callback as asynchronous: This is apparently an antipattern and there are coding problems which can arise from it. I understand that it becomes easier to fail to catch errors here, even when placing await statements inside try/catc…
Await equivalent of ‘Promise.resolve().then()’?
I’m familiar with Promises, but have inherited some rather unusual code that, rather than making a new Promise(), uses the following: From my research, this is a weird version of setImmediate – ie, run the following function on the next tick. What would be the await version of this? Answer There m…
Correct Try…Catch Syntax Using Async/Await
I like the flatness of the new Async/Await feature available in Typescript, etc. However, I’m not sure I like the fact that I have to declare the variable I’m awaiting on the outside of a try…catch block in order to use it later. Like so: Please correct me if I’m wrong, but it seems to…
Why does TypeScript use “Like” types?
Why does TypeScript have a type and then a “like type”? An example of this is Promise<T> and PromiseLike<T>. What are the differences between these two types? When should I use them? In this case why not just have one Promise type? Answer If you look at the definition files (let’…
Why would you try-catch around a promise? Does that catch the promise’s error?
I stumbled upon some code that looked off to me: If some somePromise() fails, would this not get caught, and the app would crash? Does this try-catch even do anything? Should be this, correct?: Answer TL;DR – If a function that returns a promise throws an exception before returning the promise then that…
fetch response.text() returns pending promise
I test the fetch API with jsonplaceholder URL, but my function returns “Promise State: Pending”, and I don’t understand why : I think the problem is because of asynchronous/synchronous methods? Answer I think the problem become asynchrone/synchrone method ? Yes. You’ve (mostly) correct…
Rethrowing error in promise catch
I found the following code in a tutorial: I’m a bit confused: does the catch call accomplish anything? It seems to me that it doesn’t have any effect, since it simply throws the same error that was caught. I base this on how a regular try/catch works. Answer There is no point to a naked catch and …
JavaScript array .reduce with async/await
Seem to be having some issues incorporating async/await with .reduce(), like so: The data object is logged before the this.store completes… I know you can utilise Promise.all with async loops, but does that apply to .reduce()? Answer The problem is that your accumulator values are promises – they&…