How to Array.map chain off of async await?

Question

How can I run Array.map off of an await?

const CLASS_PATH = 'User/matt/Github/project';
const PACKAGE_JSON = 'package.json';

const walk = async path => {
  let dirs = [];
  for (const file of await readdir(path)) {
    if ((await stat(join(path, file))).isDirectory()) {
      dirs = [
        ...dirs,
        file,
      ];
    }
  }
  return dirs;
};


async function main() {
  const packagePaths = await walk(CLASS_PATH)
        .map(pkgName => join(CLASS_PATH, pkgName, PACKAGE_JSON));

}
main();

I think you will find [this Q&A](https://stackoverflow.com/a/55225285/633183) relevant — Mulan, May 18 '19 at 05:58
@MatthewHarwood, can I ask what you expect `main` to do? Are you trying to find the path to all `package.json` files in a given directory? — Mulan, May 19 '19 at 19:47

score 5 · Accepted Answer · edited Feb 16 '22 at 17:01

5

Parenthesis () can always be used to change operator predescendence:

 (await walk(CLASS_PATH)).map(/*...*/)

edited Feb 16 '22 at 17:01

jbyrd

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answered May 17 '19 at 21:47

Jonas Wilms

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You sir are amazing – Armeen Moon May 17 '19 at 21:48
1

I'm surprised you did not know that, you actually used that *in your code* already. – Jonas Wilms May 17 '19 at 21:52
Cuz I copy and pasta a walk function >_ – Armeen Moon May 17 '19 at 21:58

score 0 · Answer 2 · answered May 17 '19 at 21:56

You can also use Promise. So in your case:

const packagePaths = await Promise.all(walk(CLASS_PATH).map(async (item): Promise<number> => {
    await join(CLASS_PATH, pkgName, PACKAGE_JSON);
}));

The Promise.all(iterable) method returns a promise that resolves when all of the promises in the iterable argument have resolved, or rejects with the reason of the first passed promise that rejects.

How to Array.map chain off of async await?

2 Answers2

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