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In this video, we will talk about callback.

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So let's see what we will cover on the callback in this particular video.

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First, we will explain callback with diagram and we will also talk about why do we need callback?

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And in the next video we will see how we can use callback to write async code.

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So let's get started.

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Let's say that we want to watch videos from YouTube.

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So definitely we need to talk to a server called YouTube server.

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Great.

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So the next step is that we make a request by the title of the video we want to watch, and then as

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soon as we hit enter, it sent a request to this particular server.

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Now, before getting back what we want.

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It depends on a lot of factors.

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So let's say that we are on a slow network.

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It means it going to take some time before the response or the video you want to watch will be sent

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to our browser.

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So why is this one is loading or our request is loading?

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We need an intermediate that hey please you don't worry.

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When everything is ready, the server will now send the response to me.

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Then I'll send back to you.

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So let's say that in this context we are using this robot as our callback, meaning that the callback

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is an intermediate between the actual function and what we want.

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So the robot or the callback over here is going to wait.

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So as soon as the server finished processing, then the callback would take the response or the actual

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video, and then the robot or the callback would send the response also to the browser or to the user.

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Now the user is now happy to watch the video.

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So technically, what is callback?

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Well, callback is a function that is passed to another function as an argument and this function is

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then executed after the function that is passed to eight is executed, as we saw in the diagram.

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Good.

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So in the next video you will see how we can make use of callback to write async code.