Understanding Promises in JavaScript: Overcoming Callback Hell and Inversion of Control

?? Before the advent of Promises, we relied heavily on callback functions for asynchronous operations. This often led to two major issues:

1?? Callback Hell (Pyramid of Doom): This is a situation where callbacks are nested within callbacks, leading to code that's hard to read and debug.

2?? Inversion of Control: This is when you hand over control of your code to a third party (usually a library or a third-party API). This can lead to trust issues and makes error handling difficult.

?? The introduction of Promises in JavaScript provided a solution to these problems.

?? A Promise is an object that represents the eventual completion or failure of an asynchronous operation. It has three states:

1?? Pending: The Promise's outcome hasn't yet been determined.

2?? Fulfilled: The asynchronous operation has been completed, and the Promise has a resulting value.

3?? Rejected: The asynchronous operation failed, and the Promise will never be fulfilled.

?? Once a Promise is fulfilled or rejected, it becomes immutable, meaning its state can't change.

?? We use the .then() method to schedule a callback to be run once the Promise is fulfilled or rejected.

?? To avoid the Pyramid of Doom, we can chain Promises, allowing our code to expand vertically rather than horizontally. This is done using the .then() method.

?? A common mistake developers make is forgetting to return a value during Promise chaining. Always remember to return a value, as this will be used by the next .then() in the chain.

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