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Now before we'll dive deeper
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into state, React events,
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and what we can do with all these things,
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I wanna take a closer look
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at these change handler functions,
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because at the moment in this demo application
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I have three change handler functions.
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One for the title, one for the amount, and one for the date.
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Which makes sense since I have these three state slices
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and these three main inputs.
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And of course, using this approach is also absolutely fine.
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There's nothing wrong
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with having these different change handler functions,
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but I wanna show you an alternative approach
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which you also could consider using.
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Instead of having all these
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separate change handler functions,
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you could try to create one shared change handler function.
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For that, we could create a new function
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which could be named inputChangeHandler.
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And here I'll also create an arrow function,
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but I'll now not accept the event argument.
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But instead here we could accept some identifier,
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though this name is up to you because it's your function,
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hence your parameter name.
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And then maybe a value.
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And my idea is that I can use this one single function
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for all my inputs, for all those onChange events.
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And then we can simply identify the different inputs
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with help of this identifier
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and update the correct state slice
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based on the identifier that was passed to this function
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with that value.
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So in here we could, for example, check if identifier
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is equal to, let's say, title.
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And if that's the case, we update the title state
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by calling setEnteredTitle
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and setting this equal to the new value.
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Else if it's not title, we could check if the identifier
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is maybe equal to the date here, so if it's equal to date,
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and then update the EnteredDate with the value.
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And else it must be the amount,
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and therefore we could then call setEnteredAmount
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and set as equal to value.
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So with that, I am calling
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all these state updating functions,
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but I'm now doing this
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all in one shared change handler function.
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Now we can't use this change handler function
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as a input for onChange now though.
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That won't work because as you learned,
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React will, in the end, call this function for us
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and will pass such an event object to it
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and it will definitely not pass an identifier
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and value to it.
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We're not going to get those data points
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when React calls this function.
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But we need them for this function to work correctly.
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Now what we can do here to work around this,
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is we can go to this onChange function
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and instead of passing a pointer to inputChangeHandler
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as a value to onChange,
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we can pass an arrow function to it.
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A new anonymous arrow function
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which we create down there where we need it.
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With that, it's this arrow function that will be called
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by React whenever this input changes.
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Therefore this arrow function will receive
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this event object.
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And in the body of this arrow function
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we can now manually execute inputChangeHandler.
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So execute this function here, which I just added.
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We manually execute it by adding parentheses.
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And now this code in here will not be executed
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when this line of code here is parsed,
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but instead this here will only be executed
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when this arrow function here is executed.
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And that will only be the case
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when this change event occurs.
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But now that we have this wrapper arrow function here
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we have full control
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over how inputChangeHandler will be executed.
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And we can therefore now pass our identifier
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as a first argument.
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So for example, title here,
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so that for this title input here,
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we pass title as an identifier,
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so that we make it into this if branch here.
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And as a second argument, we pass the value that changed.
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So in this case here, event.target.value,
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just as before, but now in this arrow function.
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And with that, we as a developer,
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control how this function here will be called
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by wrapping it in such a arrow function,
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which is the actual function that's passed
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as a value to the onChange prop.
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But then we control how this inner function
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will be executed when the change event occurs,
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and we can then use this generic handler function
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because now we could use this same code here,
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or almost the same code,
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on the amount input value, for example,
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and pass amount as an identifier.
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But other than that, it's the same code
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and the function that's being executed is always the same.
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And this approach simply is an alternative
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to having multiple specialized handler functions.
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As mentioned, there's nothing wrong
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with having these specialized handler functions,
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but as an alternative,
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you could consider using such shared functions.
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With that, I'll get rid of that though
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and move back to the code we had before
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with the titleChangeHandler
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and the amountChangeHandler here.
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But I definitely wanted to share this alternative
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since it is something you might see in some React projects.
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And since it is something you might want to use yourself
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in your React projects.
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