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How to correctly use async/await in JavaScript?

Asked 2 days ago
Modified yesterday
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12

I'm having trouble with async/await in JavaScript. I have a function that's supposed to fetch data from an API and then process it, but it seems like the processing is happening before the data is actually fetched. How can I make sure that the processing waits for the data?

Here's my current implementation:

async function fetchData() {
    const response = await fetch('https://api.example.com/data');
    const data = await response.json();
    processData(data); // This seems to run too early
}

Even though I'm using await, the processData() function appears to execute before the data is fully retrieved. What am I missing?

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asked 2 days ago

2 Answers

24

Your fetchData function is correct. The issue is likely in how you are calling it. An async function returns a Promise. You need to await the result of fetchData or use a .then() block where you call it.

For example, if you call it from another async function:

async function main() {
    try {
        console.log('Fetching data...');
        await fetchData();
        console.log('Data processed successfully.');
    } catch (error) {
        console.error('An error occurred:', error);
    }
}

main();

If you're not in an async context, you can use:

fetchData()
    .then(() => console.log('Data processed'))
    .catch(error => console.error('Error:', error));
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answered yesterday
8

Just to add to Maria's excellent answer, always wrap your await calls in a try...catch block. Network requests can fail for many reasons (e.g., no internet connection, server is down, invalid URL), and not catching those errors will lead to an "Uncaught (in promise)" error which can crash your application.

Here's how to properly handle errors:

async function fetchDataWithErrorHandling() {
    try {
        const response = await fetch('https://api.example.com/data');
        if (!response.ok) {
            throw new Error(`HTTP error! status: ${response.status}`);
        }
        const data = await response.json();
        processData(data);
    } catch (error) {
        console.error('Failed to fetch data:', error);
        // Handle error appropriately
    }
}

This approach ensures you catch both network errors and API response errors.

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answered yesterday