Why is this Lambda function async?

Question

This Lambda function does an http-request and then writes the data into DynamoDB. I'm wondering why the function is set asynchronously. Wouldn't it be the same if it weren't async? As far as I know, await tells the code to pause and to continue after httprequest() is done. Isn't that the same like running the code synchronously?

exports.handler = async (event) => {
    try {
        const data = await httprequest();

        for (var i = 0; i < data.d.results.length; i++){
            var iden = Date.now();
            var identifier = iden.toString();
            datestring.substring(4,6) + "-" + datestring.substring(6,8);
            
        //add to dynamodb
        var params = {
            Item: {
                id: identifier,
                date: data.d.results[i].DAY_T,
            },
        TableName: 'DB'
        };
        await docClient.put(params).promise();
        }
        
        console.log('Document inserted.');
        return JSON.stringify(data);
    } catch(err) {
        console.log(err);
        return err;
    }
};

Also, await docClient. --- To use await the function it is in needs to be async. — evolutionxbox
– evolutionxbox, Commented Oct 20, 2020 at 13:16
Not exaclty, no. await gives the JavaScript engine chance to run some other bit of JS rather than block waiting a response on the called function, just like promises. — phuzi
– phuzi, Commented Oct 20, 2020 at 13:22
developer.mozilla.org/en-US/docs/Learn/JavaScript/Asynchronous/… — Liam
– Liam, Commented Oct 20, 2020 at 13:48
Isn't that the same like running the code synchronously no, it's still async. — Liam
– Liam, Commented Oct 20, 2020 at 13:49

Jamiec · Accepted Answer · 2020-10-20 13:44:26Z

1

async/await is syntactic sugar which makes writing code look similarly to how synchronous code would be written while maintaining all of the advantages of asynchronous code.

Essentially this:

var result = await doSomethingAsync();
console.log(result);

is actually this:

doSomethingAsync().then(result => {
    console.log(result);
});

If you imagine doing lots of this it gets heavily nested very quickly. When you include error handling too, the then/catch method gets long and verbose. async/await lets you use try/catch in a more natural way - the same way you're used to for synchronous code.

Mix in the fact that your code is doing multiple await within a loop, and I'd need to build up a list of promises and do a Promise.all there too. It all gets pretty hard to write without making a mistake.

edited Oct 20, 2020 at 13:44

answered Oct 20, 2020 at 13:38

Jamiec

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