How do you call a Promise inside another Promise?

How do you call a Promise inside another Promise?

Here we need to first declare a Promise by using the Promise syntax, and we will be using the then() method for its execution and then inside that then() method we will create another promise by using the same Promise syntax as illustrated above, and then we will call our result of first inside that new Promise.

How do you use a function that returns a Promise?

2 Answers

1. You return the Promise together with all the chained then functions. If you add another then to the returned Promise, it will be added at the end of the chain.
2. A Promise tells you that it will execute at some point in time, without telling you when. The then chain will execute whenever the Promise resolves.

What happens when a Promise is returned?

If the returned promise resolves, it is resolved with an aggregating array of the values from the resolved promises, in the same order as defined in the iterable of multiple promises. If it rejects, it is rejected with the reason from the first promise in the iterable that was rejected.

Can you await a function that returns a Promise?

To recap inside a function marked as async, you are allowed to place the await keyword in front of an expression that returns a promise. When you do, the execution of the async function is paused until the promise is resolved.

How do you call a function in Promise?

So it can be as simple as that.

1. var normalizeFilePath = function (filePath) { return path.
2. var normalizeFilePath = function (filePath) { return new Promise(function (resolve, reject) { resolve( path.
3. var checkFileExistance = function (filePath) { return new Promise(function (resolve, reject) { fs.

Is Promise then blocking?

If one of the promises resolves first, the then block executes and logs the value of the resolved promise. If one of the promises rejects first, the catch block executes and logs the reason for the promise rejection.

How is a promise enforceable?

Thus, a promise may be enforceable to the extent that the promisee has incurred substantial costs, or conferred benefits, in reasonable reliance on the promise. Promissory estoppel under Section 90 of the Restatement of Contracts is the primary enforcement mechanism when action in reliance follows the promise.

How do you handle promise rejection?

We must always add a catch() , otherwise promises will silently fail. In this case, if thePromise is rejected, the execution jumps directly to the catch() method. You can add the catch() method in the middle of two then() methods, but you will not be able to break the chain when something bad happens.

Why are promises better than callbacks?

The superiority of promises over callbacks is all about trust and control. Let me explain. We generally need to use callbacks (or promises) when there is a slow process (that’s usually IO-related) that we need to perform without blocking the main program process.

Does a function returning a promise need to be async?

The word “async” before a function means one simple thing: a function always returns a promise. Other values are wrapped in a resolved promise automatically. So, async ensures that the function returns a promise, and wraps non-promises in it.

Do all async functions return a promise?

Async functions always return a promise. If the return value of an async function is not explicitly a promise, it will be implicitly wrapped in a promise. Note: Even though the return value of an async function behaves as if it’s wrapped in a Promise.resolve , they are not equivalent.

How to return a promise from a function?

1) A promise that resolves to the result of the db.post (person) request. 2) The callback passed to then (…) is executed when the db.post () call returns a response or throws an exception. 3) No idea.

How to return promise from async function in JavaScript?

As you can see, the first function returns a vanilla String value; and, the second function returns a Promise. And, when we run this TypeScript file through ts-node, we get the following terminal output:

How to make a promise out of a callback function in JavaScript?

When the getChuckNorrisFact is called, it executes the request to the API and waits for either a resolve () or a reject () statement to execute. In the callback function, you simply pass the retrieved data into the resolve or reject methods.

Why is my JavaScript not returning a promise?

If you try running the above code, the result logged will be undefined. This happens because after making a call to getResult method, it in turns calls the getPromise method which gets resolved only after 2000 ms. getResult method doesn’t wait since it doesn’t returns a promise.