Fix - Await is only valid in async function Error in NodeJS

Fix - Await is only valid in async function Error in NodeJS #

The error "await is only valid in async functions and the top level bodies of modules" occurs when the await keyword is used inside of a function that was not marked as async. To solve the error, mark the directly enclosing function as async.

Here are 2 examples of how the error occurs.

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// 👇️ Cause: Function not marked as async
function getNum() {
  // ⛔️ Error: SyntaxError: await is only valid
  // in async functions and the top level bodies of modules
  const num = await Promise.resolve(100);

  return num;
}

// 👇️ Cause: Using top level await without setting
// `type` to `module` in `package.json`
const result = await Promise.resolve(42);

The first cause of the error is - using the await keyword inside of a function that was not declared as async.

To solve this, we have to mark the directly enclosing function as async.

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// ✅ now marked as async
async function getNum() {
  const num = await Promise.resolve(100);

  return num;
}

A very common cause of the error is forgetting to set an inner function as async, e.g. the ones we pass to methods like forEach(), map(), etc.

Note that the directly enclosing function of the one that uses the await keyword has to be marked as async.

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async function loopNums() {
  const nums = [3, 5, 7];

  nums.forEach(num => {
    // ⛔️ SyntaxError: await is only valid
    // in async functions and the top level bodies of modules
    await Promise.resolve(num);
  });
}

We marked the loopNums function as async, but we're using the await keyword inside of the function we passed to the forEach() method.

Instead, we should have marked the function we passed to forEach as async.

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function loopNums() {
  const nums = [3, 5, 7];

  nums.forEach(async num => {
    await Promise.resolve(num);
  });
}

Now, the function we passed to the forEach method is async, so we are able to use the await keyword in it.

If you're trying to use the await keyword on the top level of your Node.js application, make sure to set the type attribute to module in your package.json file.

If you don't have a package.json file, create one by using the npm init -y command (only if you don't have one already).

Open the package.json file at the root directory of your project and set the type attribute to module.

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{
  "type": "module",
  // ... your other settings
}

Now you can use top level await in your Node.js code.

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const result = await Promise.resolve(42);

console.log(result); // 👉️ 42