async and await are keywords commonly used on C#. They allow you to perform async operations without the callback hell.
The “callback hell” happens when you perform multiple async operations. For each operation you need to send a callback, a function that will execute when the operation completes.
But finally async and await came to the rescue! It is on C# 4.0, ECMAScript 7 and also available on Python 3.5.
Those keywords allow you to flatten your code, but still run the operation asynchronously.
Something like this:
(function () {
fs.readFile('DATA', 'utf8', function (err, contents) {
if (err) {
return console.error(err);
}
callContentApi(contents, function (err) {
if (err) {
return console.error(err);
}
console.log('Content saved');
});
});
}());
Can be written as:
(async function () {
try {
const contents = await fs.readFile('DATA', 'utf8');
await callContentApi(contents);
console.log('Content saved');
}
catch (err) {
console.error(err);
}
}());
Now it is linear, it is easier to understand the flow of the application.
Using a Promise you can create a wait function. You can use the keyword await on functions that are async or that return a new Promise.
function wait(ms) {
return new Promise((resolve, reject) => {
setTimeout(function () {
resolve();
}, ms);
});
}
(async function () {
await wait(1000);
console.log('After a second!');
}());
See
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