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REST APIs with Express

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Async/Await in Express

2:40 with Treasure Porth

We can use JavaScript's async/await keywords to handle asynchronous actions in our code, to make sure we have our quotes data before we respond to the client.

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    We're calling this method, records.getQuotes, and 0:00
    saving the result to a variable called quotes. 0:03
    records.getQuotes reaches into our data store, gets all of the quotes, and 0:06
    returns them to us. 0:10
    Once we have all those quotes, we send them back to the client as JSON. 0:11
    At the moment, however, we're getting back an empty object. 0:15
    And this is because the getQuotes function is asynchronous. 0:18
    All the functions in the records.js module use asynchronous functions to 0:22
    closely mimic the behavior of an actual database. 0:27
    And accessing a database is an inherently asynchronous operation, 0:30
    meaning we can't be exactly sure when we're going to receive the information. 0:34
    And in the meantime, JavaScript just keeps on going without waiting for 0:38
    the data to return. 0:42
    If you're new to the topic of asynchronous JavaScript, aren't familiar with promises, 0:44
    or are totally new to async and await syntax. 0:48
    I strongly recommend checking out the resources linked in the teacher's 0:51
    notes below. 0:54
    The getQuote function returns a promise, which uses Node's readFile method to 0:55
    retrieve the data from the data.json file, then resolves the promise with that data. 1:01
    The problem here is that the res.json method ends up running before 1:07
    the getQuotes function has a chance to return any data. 1:12
    JavaScript gets to this line of code and says, well, I guess there's 1:16
    nothing in this quotes variable, and moves onto the next line of code. 1:19
    The promise never has a chance to resolve, 1:23
    and as a result, we end up sending back an empty object to the client. 1:26
    What we need is a way to tell JavaScript, hey, stop. 1:30
    Just hold on and wait for 1:33
    this information to come back before running the next line of code. 1:34
    We can do that using async and await. 1:38
    We can await any function that returns a promise, so we'll await records.getQuotes. 1:40
    This tells JavaScript to expect this method to return something, so 1:47
    it shouldn't just give up on it and move on. 1:51
    It should wait and tell this method, 1:54
    return something to execute the next line of code. 1:56
    The await function must be used inside of an async function. 1:59
    This basically lets JavaScript know, hey, inside this function, we're going to ask 2:05
    you to await some information before you speed on down the line. 2:10
    So let's save and test this out by going back to the browser. 2:13
    Refresh, and now we're returning our list of quotes. 2:17
    There is some error handling that we could still do here, but 2:21
    we'll get to that in a later video. 2:24
    We'll continue to use async and await to build out the rest of our project. 2:26
    So rest assured that we'll see and 2:30
    talk about this again if you're still feeling unsure about it. 2:32
    In the next video, we'll refactor our other get route to use our data store and 2:35
    async await. 2:39

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