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Refactor with Express Middleware
3:29Using try/catch blocks to handler errors for each route can get messy after a while. We can write a middleware function that can abstract away the try/catch block to DRY up our code.
You might be noticing by now that
our code is getting a bit long.
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All these try-catch blocks make things
verbose and kind of messy-looking.
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We can use a piece of middleware to
prevent having to use try-catch blocks for
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every single route.
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Into app JS, I've added a middleware
function called asynchandler.
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If you're following along with me,
see the teacher's notes to copy and
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paste this function.
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You don't need to worry about
the exact details of how this works.
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Remember, that's kind of the point of
using a helper function or a library.
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It abstracts complexities away for you.
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But basically, it takes in a function,
wraps it in a try-catch block,
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and passes any errors to the global error
handler we wrote in the last video.
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We can use this middleware function
instead of using try catch,
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in every single one of our code blocks.
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So I'm going to scroll down
to our post route to /quotes.
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And what we can do is,
parse our route handling callback,
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this function here,
into our asyncHandler function.
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I'll show you how that works.
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First I'm going to comment
out the post route.
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And I'll start a new one just below that.
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Now the asyncHandler is going
to be our callback function.
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When a post request is made to the home
route will run the async handler function.
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Inside the asyncHandler function
we'll parse an anonymous function.
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We'll need to parse this anonymous
function the request in response objects.
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Inside the anonymous function we can put
all our code that handles the request and
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creates a new record.
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We'll go up here, uncomment this, And
we will copy and paste this in here.
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This is exactly the code we had before,
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only asyncHandler is acting
as the middleman here.
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We're going to pass at the function
containing the function we want to run
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when the request is made.
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And it's going to call that function
inside of the try-catch blocks and
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catch errors for us.
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That way we don't have to have
a try-catch block in every single route.
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One more thing, because we want to await
the creation of a record inside of this
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anonymous function, the anonymous
function needs to be asynchronous.
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Let's do this one more time.
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We'll update the /quotes/id put route,
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only this time we'll just
modify the existing code.
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So just before my anonymous
callback function here,
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I'll wrap my async handler
function around it.
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Then I can delete the keyword try along
with its brackets, and this catch block.
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If this feels uncomfortable or
overwhelming, or you just don't feel like
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you're getting exactly what's going on,
don't worry about it.
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When you're practicing
building your own API,
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you can use try catch in every
route until you feel comfortable.
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Or just keep using this syntax and
it'll eventually sink in.
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I encourage you to update all the other
routes using the asyncHandler function,
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to get used to it.
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But also keep in mind this
isn't a necessary step.
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It's just an example of how
you can use middleware to
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save yourself from a bit
of repeating code.
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