how can i use top level `await` in nodejs

2024-06-25by@tim&@ChatGPT.Model: GPT-4o

how can i use top level await in nodejs

Using top-level await in Node.js allows you to use the await keyword outside of an async function. This feature is available in Node.js starting from version 14.8.0, but it's officially stable and more widely used in version 16 and later. Here’s how you can use top-level await in Node.js:

Ensure you're using a supported version of Node.js: Make sure your Node.js version is 14.8.0 or higher. You can check your Node.js version by running:
```
node -v
```

Use an ES module: Top-level await is supported in ES modules. You can specify an ES module by either naming your file with a .mjs extension or by adding "type": "module" in your package.json file.

Using a .mjs file:

Create a file named example.mjs:

// example.mjs
const fetchData = async () => {
    // Simulating an async operation like fetching data
    return new Promise((resolve) => setTimeout(() => resolve("Data fetched"), 1000));
};

const data = await fetchData();
console.log(data);  // Output: Data fetched

Run the file using Node.js:

node example.mjs

Using package.json with "type": "module":

Update your package.json:

{
    "type": "module"
}

Create a file named example.js:

// example.js
const fetchData = async () => {
    // Simulating an async operation like fetching data
    return new Promise((resolve) => setTimeout(() => resolve("Data fetched"), 1000));
};

const data = await fetchData();
console.log(data);  // Output: Data fetched

Run the file using Node.js:

node example.js

Dealing with CommonJS (optional): If you need to use top-level await in a CommonJS module (files with .cjs extension or default in Node.js when package.json does not specify "type": "module"), you can use an immediately-invoked async function expression (IIAFE) as a workaround:

// example.cjs
(async () => {
    const fetchData = async () => {
        // Simulating an async operation like fetching data
        return new Promise((resolve) => setTimeout(() => resolve("Data fetched"), 1000));
    };

    const data = await fetchData();
    console.log(data);  // Output: Data fetched
})();

Run the file using Node.js:

node example.cjs

By following these steps, you can effectively use top-level await in your Node.js applications.

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