What is Promise in Javascript ?

In simpler terms, a Promise in JavaScript is a way to handle things that will happen in the future, like when you wait for a response from a server or a timer to finish. It’s like a placeholder for the result of an asynchronous operation.

States of promise in Javascript :

1. Pending: The asynchronous operation hasn’t finished yet.
2. Fulfilled: The operation completed successfully, holding the result.
3. Rejected: The operation encountered an error, holding the error reason.

Imagine you’re placing an online order for a pizza.

Placing the Order (Creating a Promise):

You submit your order online. This initiates the asynchronous process of preparing your pizza.The online store creates a promise object representing the eventual completion (or failure) of your order.

Preparing the Pizza (Pending State):

The promise starts in a pending state, signifying that the order hasn’t been fulfilled yet.The kitchen staff begins preparing your pizza.

Order Successful (Fulfilled State):

If the pizza is prepared successfully:The promise transitions to a fulfilled state, holding the result — your delicious pizza!

Order Failed (Rejected State):

If there’s an issue (e.g., out of ingredients, oven malfunction):The promise transitions to a rejected state, containing the error reason (e.g., “Out of pepperoni”).

Receiving the Pizza (Consuming the Promise):

You can use then and catch methods to handle the outcome:

then (Successful Order):You receive your pizza (the resolved value from the promise).You can now enjoy it! (process the data in your code).

catch (Failed Order):You’re notified about the error (the rejection reason from the promise).You can take corrective actions, like re-ordering or choosing a different pizza.

actually what is promise.all?

In JavaScript, Promise.all is a method that lets you handle the completion of multiple promises concurrently (at the same time).

why we need promise.all?

1. Parallel Execution: Promise.all allows multiple promises to run concurrently. This can significantly improve performance compared to running each promise sequentially.
2. Aggregate Results: It gathers the results of all the promises into a single array, which you can then use in your code. This is particularly useful when you need all the results together to proceed with your task.
3. Error Handling: If any of the promises in Promise.all reject, the whole operation will reject. This makes it easy to handle errors centrally instead of checking each promise individually.

How Promise.all Works

• Input: An array (or any iterable) of promises.
• Output: A single promise that resolves when all the input promises have resolved or rejects if any input promise rejects.

Implementation in Javascript

Benefits of Promise.all

1. Efficiency: By running promises in parallel, you save time compared to running them sequentially.
2. Simplicity: It provides a clear and concise way to handle multiple promises and their results.
3. Centralized Error Handling: Any failure in the set of promises is caught in a single place, making error management easier.

Use Cases for Promise.all

• Fetching multiple API endpoints concurrently.
• Performing multiple asynchronous computations and aggregating their results.
• Waiting for several independent asynchronous operations to complete before proceeding.

In essence, Promise.all is a powerful tool for coordinating multiple asynchronous operations in JavaScript, ensuring efficient and well-structured code.