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Asynchronous Code in Express

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Reduce Error Handling Code When Using Async/Await

3:35 with Treasure Porth

Using try/catch to handle errors when using async/await syntax can get repetitive and verbose. In this video we'll look at an example of how we can use a function to abstract away try/catch.

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    If this were an application that had many routes, using a try-catch block 0:00
    each time would make our code pretty long and unwieldy after a while. 0:04
    To get around this, we can use a piece of middleware to wrap 0:09
    each of our routes automatically in a try-catch block. 0:12
    That way we won't have to explicitly write it over and over again. 0:15
    Let's write that middleware at the top of our file. 0:19
    We'll name it asyncHandler and it will take a callback. 0:22
    Inside the asyncHandler function we'll return an asynchronous function that will 0:32
    serve as our route handler's callback. 0:36
    So it'll take the req, res and next parameters. 0:38
    Inside this function, we'll put a try-catch block. 0:49
    In the try block, we'll await whatever function we've passed to the asyncHandler 0:57
    with the normal route handling parameters. 1:02
    So basically, all we're doing here is creating a function that wraps around our 1:08
    normal route handling function. 1:12
    To this function we can pass all the code we would normally pass 1:15
    in our express route handler callback. 1:18
    If this is confusing, try to stick with me until we implement this in the code and 1:20
    hopefully, it will make more sense. 1:24
    In the catch block, we'll catch any errors and render out our error page. 1:26
    The nice thing about this is that we will no longer need to include this error code 1:41
    in every single route. 1:45
    So I'll go down and delete the error handling code from the route. 1:47
    We can also get rid of the try block. 1:54
    Now let's use the asyncHandler function in our code. 1:58
    asyncHandler will become the callback in our get route. 2:01
    So I'll cut out the current callback function and move it down below, for now. 2:05
    So this is where we will call asyncHandler, and 2:13
    the code we had before becomes a callback for asyncHandler. 2:16
    So let's copy and paste it into our asyncHandler middleware. 2:21
    Let's make sure the server is running and go to the browser and 2:33
    make sure this is working. 2:36
    Looks like our page is rendering as we expected. 2:39
    Let's also make sure the error page is rendering as expected. 2:42
    And the error handling is working as expected. 2:54
    There you have it. 2:57
    You're express route is handling asynchronous code in a maintainable, 2:58
    easy to read way. 3:01
    Let's finish up by adding a comment indicating that this is an example of 3:03
    using async/await I 3:06
    encourage you to give all this information a bit of time to sink in. 3:12
    Especially if you're newer to the subject. 3:16
    Asynchronous programming is a very difficult topic. 3:19
    Don't be afraid to use these approaches without completely 3:22
    understanding how they work. 3:24
    That's perfectly normal, and you'll learn more and more as you work with and 3:26
    struggle with them. 3:29
    Thing will begin to click. 3:31
    Stick with it. 3:32
    And until next time, happy coding. 3:33

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