JavaScript Promises | JavaScript Promises Explained | JavaScript Tutorial For Beginners |Simplilearn

1. What’s in it for you?

2. Why does JavaScript use promises and what exactly is a promise? Don’t worry! I’ll help you with it. I’ll tell you why Promises were introduced and explain their functionality

3. Why JavaScript Promises? JavaScript is predominantly single threaded. This makes it slow and restrictive With the help of promises and other Asynchronous concepts, JavaScript can perform long network requests simultaneously without blocking the main thread

4. What’s in it for you? Click here to watch the video

5. What are JavaScript Promises? A promise is an asynchronous action that may complete at some point in the future and produce a value It notifies the user when its value is available Promises provide a robust way to wrap the result of asynchronous work, overcoming the problem of deeply nested callbacks

6. What are JavaScript Promises? States of Promises Pending: The underlying operation has not yet completed Fulfilled: The operation has finished, and the promise is fulfilled with a value Rejected: An error has occurred during the operation, and the promise is rejected with a reason A promise is an asynchronous action that may complete at some point in the future and produce a value It notifies the user when its value is available Promises provide a robust way to wrap the result of asynchronous work, overcoming the problem of deeply nested callbacks

7. What are JavaScript Promises? States of Promises Pending: The underlying operation has not yet completed Fulfilled: The operation has finished, and the promise is fulfilled with a value Rejected: An error has occurred during the operation, and the promise is rejected with a reason A Promise is said to be settled when it is either fulfilled or rejected Once a promise is settled, it becomes immutable, and its state cannot change then(callback) – Used to attach a callback when the promise is resolved/fulfilled catch(callback) – Used to attach a callback when the promise is rejected

8. What are JavaScript Promises? A Promise is said to be settled when it is either fulfilled or rejected Once a promise is settled, it becomes immutable, and its state cannot change then(callback) – Used to attach a callback when the promise is resolved/fulfilled catch(callback) – Used to attach a callback when the promise is rejected

9. What are JavaScript Promises? Return Asynchronous action .then(callback) (Fulfilled) Yes Action successful? Async. Action New Promise (pending) end No .catch(callback) (Rejected) Error handling Return

10. What are JavaScript Promises? Return Asynchronous action .then(callback) (Fulfilled) General Syntax: let some_action = new Promise(function(resolve, reject) { // Perform some work }) Yes Action successful? Async. Action New Promise (pending) end No .catch(callback) (Rejected) Error handling Return