async/await in node.js: error handling

So, let's have a quick look at async await error handling!

	(async function() {
	try {
	await Promise.reject('test')
	} catch (err) {
	console.error('bwoke', err)
	}
	})()

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Like last time we are wrapping our code in a self-executing function so we can use the async keywords.

To handle errors in async functions we use a try-catch block like we normally would in synchronous code. You can see from the example that a rejected promise comes out of our catch block.

	function throwPromise() {
	return new Promise((resolve, reject) => {
	throw new Error('An error happened inside the promise, but not rejected')
	})
	}
	throwPromise()
	.then(() => {
	console.log("This won't get executed")
	})
	.catch(err => {
	console.log('This handles the thrown error')
	})

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As we know from previous posts a promise will be rejected if reject() is called or an error is thrown inside of the promise.

	async function rejected() {
	throw 'error'
	}
	(async function() {
	try {
	await rejected()
	} catch (err) {
	console.error('bwoke', err)
	}
	})()

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Also if you throw an error in an async function this results in a rejected promise. So you can see now how it all fits together, any promise rejections or errors thrown result in the catch block being used.

	(async function() {
	try {
	Promise.reject('test')
	await Promise.reject('test 2')
	} catch (err) {
	console.error('bwoke', err)
	}
	})()

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Just worthy to note that non-awaited rejected promises will not trigger the catch block but will put up an unhandled promise rejection error.