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REST APIs with Express

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Refactor with Express Middleware

3:29 with Treasure Porth

Using 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.

Snippet

function asyncHandler(cb){
  return async (req, res, next)=>{
    try {
      await cb(req,res, next);
    } catch(err){
      next(err);
    }
  };
}

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    You might be noticing by now that our code is getting a bit long. 0:00
    All these try-catch blocks make things verbose and kind of messy-looking. 0:03
    We can use a piece of middleware to prevent having to use try-catch blocks for 0:07
    every single route. 0:12
    Into app JS, I've added a middleware function called asynchandler. 0:13
    If you're following along with me, see the teacher's notes to copy and 0:18
    paste this function. 0:21
    You don't need to worry about the exact details of how this works. 0:22
    Remember, that's kind of the point of using a helper function or a library. 0:25
    It abstracts complexities away for you. 0:29
    But basically, it takes in a function, wraps it in a try-catch block, 0:31
    and passes any errors to the global error handler we wrote in the last video. 0:37
    We can use this middleware function instead of using try catch, 0:42
    in every single one of our code blocks. 0:46
    So I'm going to scroll down to our post route to /quotes. 0:49
    And what we can do is, parse our route handling callback, 0:54
    this function here, into our asyncHandler function. 0:59
    I'll show you how that works. 1:03
    First I'm going to comment out the post route. 1:04
    And I'll start a new one just below that. 1:08
    Now the asyncHandler is going to be our callback function. 1:14
    When a post request is made to the home route will run the async handler function. 1:18
    Inside the asyncHandler function we'll parse an anonymous function. 1:25
    We'll need to parse this anonymous function the request in response objects. 1:33
    Inside the anonymous function we can put all our code that handles the request and 1:41
    creates a new record. 1:46
    We'll go up here, uncomment this, And we will copy and paste this in here. 1:51
    This is exactly the code we had before, 1:58
    only asyncHandler is acting as the middleman here. 2:00
    We're going to pass at the function containing the function we want to run 2:03
    when the request is made. 2:07
    And it's going to call that function inside of the try-catch blocks and 2:08
    catch errors for us. 2:13
    That way we don't have to have a try-catch block in every single route. 2:14
    One more thing, because we want to await the creation of a record inside of this 2:18
    anonymous function, the anonymous function needs to be asynchronous. 2:23
    Let's do this one more time. 2:30
    We'll update the /quotes/id put route, 2:32
    only this time we'll just modify the existing code. 2:35
    So just before my anonymous callback function here, 2:38
    I'll wrap my async handler function around it. 2:42
    Then I can delete the keyword try along with its brackets, and this catch block. 2:50
    If this feels uncomfortable or overwhelming, or you just don't feel like 3:00
    you're getting exactly what's going on, don't worry about it. 3:04
    When you're practicing building your own API, 3:07
    you can use try catch in every route until you feel comfortable. 3:09
    Or just keep using this syntax and it'll eventually sink in. 3:12
    I encourage you to update all the other routes using the asyncHandler function, 3:16
    to get used to it. 3:20
    But also keep in mind this isn't a necessary step. 3:21
    It's just an example of how you can use middleware to 3:24
    save yourself from a bit of repeating code. 3:27

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