How do I use then in node JS?

What is then in node JS?

then() The then() method returns a Promise . It takes up to two arguments: callback functions for the success and failure cases of the Promise . const promise1 = new Promise((resolve, reject) => { resolve(‘Success!’); }); promise1.then((value) => { console.log(value); // expected output: “Success!”

What is then () in JS?

The then() method in JavaScript has been defined in the Promise API and is used to deal with asynchronous tasks such as an API call. Previously, callback functions were used instead of this function which made the code difficult to maintain.

What is the function of then?

Use the then function to access the eventual result of a promise (or, if the operation fails, the reason for that failure). Regardless of the state of the promise, the call to then is non-blocking, that is, it returns immediately; so what it does not do is immediately return the result value of the promise.

What is Promise then?

A promise is a pattern for handling asynchronous operations. The promise allows you to call a method called “then” that lets you specify the function(s) to use as the callbacks.

What is Node JS promise example?

A Node. js Promise is a placeholder for a value that will be available in the future, allowing us to handle the result of an asynchronous task once it has completed or encountered an error. Promises make writing asynchronous code easier. They’re an improvement on the callback pattern and very popular in Node.

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Why is node js single threaded?

js follows Single-Threaded with Event Loop Model inspired by JavaScript Event-based model with JavaScript callback mechanism. So, node. js is single-threaded similar to JavaScript but not purely JavaScript code which implies things that are done asynchronously like network calls, file system tasks, DNS lookup, etc.

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.

What does by then mean?

“By then” means that the action will not be a continuous action. It will be an action for a specific moment and it can be done at any time from now to “until then”.

How do you get a promise value?

Promises are theoretically their own objects. they contain a result which can be accessed through the success function of the promise. So if you want to work with the return value of a promise’s asynchronous callback, it has to be done inside another asynchronous callback.

How does promise chaining work?

Promises chaining

  1. The initial promise resolves in 1 second (*) ,
  2. Then the . then handler is called (**) , which in turn creates a new promise (resolved with 2 value).
  3. The next then (***) gets the result of the previous one, processes it (doubles) and passes the next handler.
  4. … and so on.