Exploring the concept of promises further, I decided to create a simple async delay function that incorporates a timeout feature:
const app = express();
function timeout(duration) {
return new Promise((resolve, reject) =>
setTimeout(() => {
console.log('timeout complete');
resolve('promise returned');
}, duration)
);
}
async function delay(duration) {
let returnedPromise = await timeout(duration);
console.log(returnedPromise);
}
app.get('/', (req, res) => {
res.send(`Performance example: ${process.pid}`);
});
app.get('/timer', async (req, res) => {
await delay(5000);
res.send(`Ding ding sing! ${process.pid}`);
});
console.log('Worker process initiated.');
app.listen(3000);
The function works as intended and responds after a 5-second delay.
However, when I modify the app.get('/timer') route in this way, the promise remains unresolved:
app.get('/timer', (req, res) => {
async () => {
await delay(5000);
res.send(`Ding ding ding! ${process.pid}`);
};
});
I am puzzled by why moving the async keyword from outside the callback to within the callback causes this issue.
EDIT:
I forgot to invoke the function :) The correct implementation is as follows:
app.get('/timer', (req, res) => {
(async () => {
await delay(5000);
res.send(`Ding ding ding! ${process.pid}`);
})();
});