Promises and async-await

Author: learning-zone

README.md

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-#### Q. ***What is difference between promise and async await in Node.js?***
+## Q. ***What is difference between promises and async-await in Node.js?***
+
+**1. Promises**
+
+A promise is used to handle the asynchronous result of an operation. JavaScript is designed to not wait for an asynchronous block of code to completely execute before other synchronous parts of the code can run. With Promises, we can defer the execution of a code block until an async request is completed. This way, other operations can keep running without interruption.
+
+**States of Promises:**
+
+* `Pending`: Initial State, before the Promise succeeds or fails.
+* `Resolved`: Completed Promise
+* `Rejected`: Failed Promise, throw an error
+
+*Example:*
+
+```js
+function logFetch(url) {
+  return fetch(url)
+    .then(response => {
+      console.log(response);
+    })
+    .catch(err => {
+      console.error('fetch failed', err);
+    });
+}
+```
+
+**2. Async-Await**
+
+`Await` is basically syntactic sugar for **Promises**. It makes asynchronous code look more like synchronous/procedural code, which is easier for humans to understand.
+
+Putting the keyword `async` before a function tells the function to return a Promise. If the code returns something that is not a `Promise`, then JavaScript automatically wraps it into a resolved promise with that value. The `await` keyword simply makes JavaScript wait until that `Promise` settles and then returns its result.
+
+*Example:*
+
+```js
+async function logFetch(url) {
+  try {
+    const response = await fetch(url);
+    console.log(response);
+  }
+  catch (err) {
+    console.log('fetch failed', err);
+  }
+}
+```
+
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+
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