Readings: Async/Await

Below you will find some reading material, code samples, and some additional resources that will help you to better understand asynchronous Javascript, specifically Promises

Javascript Async/Await Pattern

Promises, although a big improvement over Callbacks for asynchronous functionality, still have a slightly messy syntax that can be confusing, especially when nesting. With ES6, Javascript introduced the async / await pattern to add even more syntactic sugar on promises.

Here’s a simple function that returns a promise, and a standard call that invokes that function, and uses .then() and .catch() to interact with it.

function goAndGetSomeData() {
  return new Promise( (resolve,reject) => {
    if( true ) {
      resolve("It totall worked!");
    }
    else {
      reject("Failure is always an option...");
    }
  })
}

goAndGetSomeData(params)
  .then( someData => {
    // do something with someData
  })
  .catch( error => {
    // do something with the error
  });

Here’s another way to call that function, but using an async function instead of the .then() syntax…You simply tag a function as async and then within it, await the promise to happen. Effectively, the variable you assign to the await is the same thing you would have gotten in a .then() callback. This just looks a lot nicer.

async function getData() {
  let someData = await goAndGetSomeData()
  // do something with someData
}

getData();

Handling Errors can be done in 2 ways.

  1. If you want to handle the error in the async function, you wrap the call in a try{}/catch()

    async function getData() {
      try {
        let someData = await goAndGetSomeData()
        // do something with someData
      } catch(error) {
        // handle the error
      }
    }
    
    getData()
    

Alternatively, you can handle the error in the code that calls your function, you can deal with it as you please outside of the async function call.

   async function getData() {
      let someData = await goAndGetSomeData()
      // do something with someData
   }

   getData().catch(error => console.log(error));

Additional Resources