I have a simple script trying to test out top level await with Node & TypeScript.

import { readFile } from "fs/promises";

async function getNum(filename: string) {
  return parseInt(await readFile(filename, "utf8"), 10);
}

try {
  const numberPromises = [1, 2, 3].map((i) => getNum(`${i}.txt`));
  const numbers = await Promise.all(numberPromises);
  console.log(numbers[0], numbers[1], numbers[2]);
} catch (err) {
  console.error("Something went wrong");
  console.error(err);
}

I get this error when I try to compile with TypeScript:

error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', or 'nodenext', and the 'target' option is set to 'es2017' or higher.

It's triggered by the top-level await on line9:

const numbers = await Promise.all(numberPromises);

I'm confused because I have done both of the things mentioned in the error message and I have tried to pair down my tsconfig.json as much as possible.

{
  "compilerOptions": {
    "module": "es2022",
    "target": "es2017",
    "outDir": "dist",
    "strict": true,
    "moduleResolution": "Node"
  }
}

I also have type: module in my package.json file.

{
  "name": "ts-test",
  "version": "1.0.0",
  "type": "module",
  "devDependencies": {
    "@types/node": "^17.0.5",
    "typescript": "^4.6.0-dev.20211226"
  },
  "scripts": {
    "dev": "node dist/script.js",
    "compile": "tsc script.ts"
  },
  "author": "Todd Matthews",
  "license": "ISC",
  "volta": {
    "node": "17.3.0"
  }
}

Any help on how I could test out top-level await with Node and TypeScript would be greatly appreciated!

CodePudding user response：

I'll provide a simpler reproduction case for you which doesn't rely on any filesystem API, and I'll include all repo files and commands:

Files

./package.json:

{
  "name": "so-70491077",
  "version": "1.0.0",
  "description": "",
  "type": "module",
  "main": "dist/main.ts",
  "scripts": {
    "test": "tsc && node dist/main.js"
  },
  "author": "",
  "license": "MIT",
  "devDependencies": {
    "typescript": "^4.5.4"
  }
}

./tsconfig.json:

{
  "compilerOptions": {
    "module": "es2022",
    "target": "es2017",
    "outDir": "dist",
    "strict": true,
    "moduleResolution": "Node"
  },
  "files": ["main.ts"]
}

./main.ts:

export async function getRandom (): Promise<number> {
  return Math.random();
}

const n = await getRandom();
console.log(n);

Commands

cd /path/to/the/dir/where/you/stored/the/files/above
npm i
npm test

Output

> [email protected] test
> tsc && node dist/main.js

0.9303778211654203 # a similar floating point number

CodePudding user response：

Your code and the tsconfig.json are fine. But tsc doesn't use tsconfig.json file. From the doc What is a tsconfig.json:

When input files are specified on the command line, tsconfig.json files are ignored.

So, don't specify the input files for the compile npm script.

"scripts": {
   "compile": "tsc"
}