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You might get another question regarding the Sinclair's jealous group, for example, right in the synchronous

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function of which executes Colbeck after finishing, it's a synchronous task.

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And actually, if you don't know in JavaScript, where using callbacks quite a lot and previously before

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promises and disintegrate, we used callback for fetch and data.

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Also even now, callback is quite popular way to work inside the application.

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So actually, first of all, we want to write some function which will make some asynchronous code.

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And the easiest way to simulate in JavaScript asynchronous code is by using set timeout because, for

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example, were fetching some data from the backend and it takes time.

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This is why I want to create here a sink function, and they just name it as a fan.

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And here we want to get our callback as a parameter and actually callback is just a function.

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But the most important part is that the synchronous function doesn't know what callback is.

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It can be whatever because we're calling it from outside.

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Now inside we are doing some asynchronous code, for example, would fetch data from a page or in our

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case, here we're using set timeout to simulate this.

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And we have set timeout, for example, for two seconds.

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And then at the end, we want to call our callback.

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This is why we simply call this function or sometimes with the data as the result of our API.

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Maybe.

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So here we can write code back done.

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And this is it.

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Our asynchronous function is ready.

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Now how are using this function?

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We just tried to sync function and we are providing our callback and said this is a function which will

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be executed inside at the end.

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This is why here we can see that we are getting the function with the argument message.

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This is what we are getting back from our async function.

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In here we can write console.log, callback and here comma message.

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And let's check if it's working.

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I'm reloading the page.

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And as you can see, we don't hear anything now after two seconds were getting called back done.

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This is exactly how callbacks are working and this is exactly what we implemented.

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So we have in the synchronous function, which executes callback after finishing, it's a synchronous

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task.

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And the second question that you might get here, what problem callback solve.

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And actually, there are two important points.

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First of all, Colback, allow us to make some assume control staff and wait for the result because

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actually here we're just providing the function from outside.

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And it will be called later and not immediately.

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This is the main purpose of the callback.

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And secondly, it's important to remember that inside our asynchronous function of we don't know what

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this callback.

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This is why we can build shareable things.

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This callback can do whatever in different cases.

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For example, on the one page, we want to fetch data and maybe render this data, and on another page,

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we want to fetch this data and calculate the total number of posts or something like this, which actually

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means callback is a generic function.

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This is why we can easily share our asynchronous function without specific implementation of our callback.