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[00:00 - 00:08] In this lesson, we are going to explore a little bit of history of how RxJS came to be. Initially, developers utilized callback functions.
[00:09 - 00:19] Those are just functions that you pass as parameters to other functions to be executed once a task is finished. However, this approach quickly revealed several drawbacks.
[00:20 - 00:27] The first one is readability and maintainability. It becomes clear that this structure is very hard to read and I also maintain.
[00:28 - 00:34] The second drawback is error handling. You see how quickly it becomes very unpleasant to do error handling.
[00:35 - 00:39] And the last one is debugging. This structure is actually called callback hell.
[00:40 - 00:45] Now, in order to solve this problem, smart people came up with promises. So, what are promises?
[00:46 - 00:59] Promises are objects that denote the potential completion or failure of asynchronous operation. The ability to change results from preceding functions enhances code readability offers a cleaner structure and mitigates the callback hell.
[01:00 - 01:05] This is what the promise looks like. So, you will call your function which will return a promise.
[01:06 - 01:11] Once the promise resolves, you can call another function with its output. And so forth and so forth.
[01:12 - 01:18] So, basically, this part here does the same as in the previous one. Except, now it has solved a few problems.
[01:19 - 01:28] So, this structure becomes more readable. It's a lot easier to maintain, debug and also handle any errors that rise from handling a promise.
[01:29 - 01:37] However, promises come with their own set of limitations. They are not cancelable, meaning once initiated, a promise will run to completion.
[01:38 - 01:45] Additionally, promises execute immediately upon creation, which isn't always desirable. Later, async/await came to be.
[01:46 - 01:53] Async/await is built on top of promises. And it's actually syntactic sugar for promises.
[01:54 - 02:02] This is what it looks like. And for people that know languages like C# or Python, this syntax looks very familiar.
[02:03 - 02:11] The advantage of async/await is that it makes asynchronous code look synchronous. And also, it proves readability, maintainability and error handling.
[02:12 - 02:20] But unfortunately, async/await doesn't really solve the problem that promises have. So, they have the same drawbacks as promises do.
[02:21 - 02:27] And so, there is no cancellation mechanism. And also, once a function is executed, it executes immediately.
[02:28 - 02:36] So, there is no way to delay this. Later on, people came up with RxJS, which is short for reactive extension for JavaScript.
[02:37 - 02:43] This is what it looks like. It does the exact same thing as the previous async/await or promise that you've seen.
[02:44 - 02:57] For those of you who are not familiar with observables, subscriptions, I promise, by the end of this course, you will feel very comfortable in using observables and subscriptions and working with RxJS.